Distortion compensation apparatus and distortion compensation method

ABSTRACT

A distortion compensation apparatus for performing distortion compensation processing by applying the inverse properties of distortion properties of the power amplifier to a transmission signal to be input to a power amplifier, includes a plurality of distortion compensation coefficient storage units configured to store a plurality of distortion compensation coefficients used for the distortion compensation processing, an offset correction processing unit configured to subject the distortion compensation coefficient stored in each of the plurality of distortion compensation coefficient storage units to offset correction processing, and to generate distortion compensation coefficients in the case that the offset correction processing has not been performed, corresponding to plurality of distortion compensation coefficient storage units, in a pseudo manner and a distortion compensation processing unit configured to subject the transmission signal to the distortion compensation processing based on the distortion compensation coefficients generated in a pseudo manner.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2011-102451, filed on Apr. 28,2011, the entire contents of which are incorporated herein by reference.

FIELD

A technique disclosed in one aspect of embodiments of the presentdisclosure relates to a distortion compensation apparatus and adistortion compensation method.

BACKGROUND

With wireless communication devices in wireless communication systems,high efficiency has strongly been demanded from a viewpoint such asreduction in device size, and energy saving.

Power amplifiers in wireless communication devices are generally used ata high-efficiency saturation region. However, it has been recognizedthat in the event that a power amplifier is used around a saturationregion, nonlinear distortion increases. As for a technique for reducingadjacent channel leakage power (Adjacent Channel Power, ACP) whilesuppressing this nonlinear distortion, there is distortion compensationprocessing. A distortion compensation apparatus configured to performdistortion compensation processing is included in wireless communicationdevices. As for distortion compensation apparatuses, there is a deviceemploying a method such as series type or look up table (hereafter,referred to be as LUT) type, or the like.

On the other hand, with power amplifiers, it has been recognized that aphenomenon such as memory effect occurs. The memory effect is aphenomenon wherein, with a power amplifier, an output signal as to aninput signal at certain point-in-time is influenced by an input signalin the past. Accordingly, a power amplifier has been desired whereinnonlinear distortion in the above power amplifier can be compensated,and also influence of memory effect in a power amplifier can becompensated.

Note that U.S. Pat. No. 7,561,636 has disclosed an example of adistortion compensation apparatus including multiple LUT. Also, JapaneseLaid-open Patent Publication No. 2007-019782 has disclosed a techniquefor obtaining the offset of a distortion compensation coefficient storedin a LUT, and performing distortion compensation processing using adistortion compensation coefficient obtained by subtracting this offset.

SUMMARY

According to an aspect of the invention, a distortion compensationapparatus for performing distortion compensation processing by applyingthe inverse properties of distortion properties of said power amplifierto a transmission signal to be input to a power amplifier, includes aplurality of distortion compensation coefficient storage unitsconfigured to store a plurality of distortion compensation coefficientsused for said distortion compensation processing, an offset correctionprocessing unit configured to subject said distortion compensationcoefficient stored in each of said plurality of distortion compensationcoefficient storage units to offset correction processing, and togenerate distortion compensation coefficients in the case that saidoffset correction processing has not been performed, corresponding tosaid plurality of distortion compensation coefficient storage units, ina pseudo manner and a distortion compensation processing unit configuredto subject said transmission signal to said distortion compensationprocessing based on said distortion compensation coefficients generatedin a pseudo manner.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an example of the internalconfiguration of a multi-LUT-type distortion compensation apparatus;

FIGS. 2A and 2B are diagrams illustrating an example of thedistributions of the distortion compensation coefficients at LUTs (LookUp Tables) after distortion compensation processing and updatingprocessing of the distortion compensation coefficients during a certainperiod of time at the distortion compensation apparatus;

FIG. 3 is a diagram illustrating an example of the configuration of awireless communication device including a multi-LUT-type distortioncompensation apparatus according to a first embodiment;

FIG. 4 is a diagram illustrating an example of the internalconfiguration of a pre-distortion signal generating unit according tothe first embodiment;

FIG. 5 is a diagram for describing distortion compensation coefficientcorrection processing at the pre-distortion signal generating unitaccording to the first embodiment;

FIG. 6 is a diagram illustrating an example of a flowchart of distortioncompensation coefficient correction and updating processing at thedistortion compensation apparatus according to the first embodiment;

FIG. 7 is a diagram illustrating an example of the internalconfiguration of a pre-distortion signal generating unit according to asecond embodiment;

FIG. 8 is a diagram illustrating an example of a flowchart of distortioncompensation coefficient correction and updating processing at adistortion compensation apparatus according to the second embodiment;

FIG. 9 is a diagram illustrating an example of the internalconfiguration of a pre-distortion signal generating unit according to athird embodiment;

FIG. 10 is a diagram illustrating an example of a flowchart ofdistortion compensation coefficient correction and updating processingat a distortion compensation apparatus according to the thirdembodiment;

FIG. 11 is a diagram illustrating an example of the internalconfiguration of a pre-distortion signal generating unit according to afourth embodiment;

FIG. 12 is a diagram for describing distortion compensation coefficientcorrection processing at the pre-distortion signal generating unitaccording to the fourth embodiment;

FIG. 13 is a diagram illustrating an example of a flowchart ofdistortion compensation coefficient correction and updating processingat a distortion compensation apparatus according to the fourthembodiment;

FIG. 14 is a diagram illustrating an example of the internalconfiguration of a pre-distortion signal generating unit according to afifth embodiment;

FIG. 15 is a diagram for describing division processing of an addressregion to be corrected at each LUT in the pre-distortion signalgenerating unit according to the fifth embodiment; and

FIG. 16 is a diagram illustrating an example of a flowchart ofdistortion compensation coefficient correction and updating processingat a distortion compensation apparatus according to the fifthembodiment.

DESCRIPTION OF EMBODIMENTS

Hereafter, embodiments of the present disclosure will be described.

EMBODIMENTS

As for a distortion compensation apparatus capable of compensatingdistortion due to memory effect in addition to nonlinear distortion at apower amplifier while suppressing increase in circuit scale, there is amulti-LUT-type distortion compensation apparatus. The multi-LUT-typedistortion compensation apparatus includes multiple LUT, and generates apre-distortion signal by performing distortion compensation processingbased on multiple distortion coefficients stored in the multiple LUT anda transmission signal.

FIG. 1 is a diagram illustrating an example of the internalconfiguration of a multi-LUT-type distortion compensation apparatus 100.As illustrated in FIG. 1, a pre-distortion signal generating unit 130 ofthe distortion compensation apparatus 100 includes an address generatingunit 102, a delay unit 104, a LUTa (Look Up Table) 106, a LUTb 108, aLUTc 110, a LUTd 112, adders 114 and 116, multipliers 118 and 120, adelay unit 122, and an adder 124.

The address generating unit 102 receives a transmission signal Tx(t),and generates an address Adrs(Tx(t)) corresponding to the power valuep(t) of the transmission signal Tx(t). The generated address Adrs(Tx(t))is supplied to the LUTa 106 and LUTc 110.

The delay unit 104 receives the address Adrs(Tx(t)) generated by theaddress generating unit 102. The delay unit 104 outputs the receivedaddress Adrs(Tx(t)) by delaying output by time equivalent to differencebetween the current reference point-in-time and the previous referencepoint-in-time, thereby generating an address Adrs(Tx(t−1)) correspondingto the power value p(t−1) of the transmission signal Tx(t−1) at theprevious reference point-in-time t−1. The generated addressAdrs(Tx(t−1)) is supplied to the LUTb 108 and LUTd 112.

The LUTa 106 received the address Adrs(Tx(t)), and reads out adistortion compensation coefficient ha(p(t)) from the location indicatedby the received address Adrs(Tx(t)). The LUTa 106 supplies the readdistortion compensation coefficient ha(p(t)) to the adder 114. In thesame way, the LUTc 110 receives the address Adrs(Tx(t)) to supply adistortion compensation coefficient hc(p(t)) to the adder 116.

The LUTb 108 receives the address Adrs(Tx(t−1)), and reads out adistortion compensation coefficient hb(p(t−1)) from the locationindicated by the received address Adrs(Tx(t−1)). The LUTb 108 suppliesthe read distortion compensation coefficient hb(p(t−1)) to the adder114. In the same way, the LUTd 112 receives the address Adrs(Tx(t−1)) tosupply a distortion compensation coefficient hd(p(t−1)) to the adder116.

The adder 114 performs synthesis by adding the distortion compensationcoefficients ha(p(t)) and hb(p(t−1)) to generate a post-synthesiscoefficient h1(p(t)). The adder 114 supplies the post-synthesiscoefficient h1(p(t)) to the multiplier 118.

The adder 116 performs synthesis by adding the distortion compensationcoefficients hc(p(t)) and hd(p(t−1)) to generate a post-synthesiscoefficient h2(p(t)). The adder 116 supplies the generatedpost-synthesis coefficient h2(p(t)) to the multiplier 120.

The multiplier 118 receives the transmission signal Tx(t) andpost-synthesis coefficient h1(p(t)). The multiplier 118 multiplies thetransmission signal Tx(t) and post-synthesis coefficient h1(p(t)),thereby generating a transmission signal Tx1(t). The multiplier 118supplies the generated transmission signal Tx1(t) to the adder 124.

The delay unit 122 outputs the transmission signal Tx(t) by delayingoutput by time equivalent to difference between the current referencepoint-in-time and the previous reference point-in-time, therebygenerating a transmission signal Tx(t−1) at the previous referencepoint-in-time t−1. The delay unit 122 supplies the generatedtransmission signal Tx(t−1) to the multiplier 120.

The multiplier 120 receives the transmission signal Tx(t−1) andpost-synthesis coefficient h2(p(t)). The multiplier 120 multiplies thetransmission signal Tx(t−1) and post-synthesis coefficient h2(p(t)),thereby generating a transmission signal Tx2(t). The multiplier 118supplies the generated transmission signal Tx2(t) to the adder 124.

The adder 124 adds the transmission signals Tx1(t) and Tx2(t), therebygenerating a pre-distortion signal PD(t). The pre-distortion signalPD(t) is a signal generated by subjecting the transmission signal Tx(t)input to the distortion compensation apparatus 100 to distortioncompensation processing, and is a transmission signal after thedistortion compensation processing.

A distortion compensation coefficient updating unit 140 receives thepre-distortion signal PD(t) and a feedback signal Fb(t), and alsoreceives the distortion compensation coefficients ha(p(t)), hb(p(t−1)),hc(p(t)), and hd(p(t−1)) from the LUTa 106, LUTb 108, LUTc 110, and LUTd112 respectively. The feedback signal Fb(t) is a feedback signalgenerated based on the output signal of a power amplifier notillustrated.

The distortion compensation coefficient updating unit 140 calculates anupdated value corresponding to the received distortion compensationcoefficient as to each of the look up tables (LUT) based on the receivedpre-distortion signal PD(t) and feedback signal Fb(t). The distortioncompensation coefficient updating unit 140 updates the distortioncompensation coefficient correlated with the power value of thetransmission signal corresponding to the received distortioncompensation coefficient based on the calculated updated value at eachLUT.

As described above, with the multi-LUT-type distortion compensationapparatus 100, the delay units 104 and 122 are provided, and correctioncomponents of the distortion compensation processing called as delayterms are generated, thereby reflecting the information of thetransmission signal Tx(t−1) at the previous reference point-in-time t−1on the distortion compensation processing as to the transmission signalTx(t), and accordingly, distortion due to memory effect of the poweramplifier can be compensated in addition to nonlinear distortion by thedistortion compensation processing.

FIGS. 2A and 2B are diagrams illustrating an example of distortioncompensation coefficient distributions at the LUTa and LUTb after thedistortion compensation processing and updating processing of thedistortion compensation coefficients is performed during a certainperiod of time at the distortion compensation apparatus 100. FIG. 2Arepresents the distribution of the distortion compensation coefficientat the LUTa 106, and FIG. 2B represents the distribution of thedistortion compensation coefficient at the LUTb 108. The vertical axisrepresents the value of a real portion (I-channel component) orimaginary portion (Q-channel component) of a distortion compensationcoefficient, and the horizontal axis represents the correspondingaddress within a LUT.

The present application inventor has found that, as illustrated in FIGS.2A and 2B, when performing updating of distortion compensationcoefficients at the distortion compensation apparatus 100, in the eventthat a distortion compensation coefficient has a certain offset at oneLUT of the LUTa and LUTb, even at the other LUT, the distortioncompensation coefficient consequently has an offset in the oppositedirection of the offset generated at one LUT so as to compensate thecertain offset thereof.

It can be conceived as an example that this phenomenon is influenced bydistortion compensation processing as to the transmission signal Tx(t)using the post-synthesis coefficient h1(p(t)) obtained by adding thedistortion compensation coefficient ha(p(t)) output from the LUTa, andthe distortion compensation coefficient hb(p(t−1)) output from the LUTbat the multiplier 118.

As a result thereof, a problem is caused wherein, in the event ofupdating of a distortion compensation coefficient advancing, thedistortion compensation coefficient converges exceeding a limitedcoefficient setting range settable at each LUT with the distortioncompensation coefficient distributions at the LUTa and LUTb. Therefore,the distortion compensation coefficient is clipped to the upper limit orlower limit in a limited coefficient setting range, and the distortioncompensation performance deteriorates.

For example, in the event that the distortion compensation coefficienthas an offset in the plus direction by updating operation at the LUTa,the offset of the distortion compensation of the LUTa is an offset inthe plus direction, and accordingly, the value of the distortioncompensation coefficient attempts to converge at the LUTb so as tomutually compensate the offsets, i.e., so as to reduce the offset thatoccurs at the post-synthesis coefficient h1(p(t)). Therefore, the offsetin the minus direction of the opposite direction of the offset in theplus direction at the LUTa consequently occurs on the distortioncompensation coefficient at the LUTb.

Accordingly, with the distortion compensation coefficient distributionsat the LUTa and LUTb, in the event of updating of the distortioncompensation coefficient advancing, operation is performed so as tomutually compensate the offsets, and accordingly, the distortioncompensation coefficient stored in the LUTa increases while having anoffset in the plus direction, and the distortion compensationcoefficient stored in the LUTb decreases while having an offset in theopposite minus direction.

As a result thereof, as illustrated in FIGS. 2A and 2B, with thedistortion compensation coefficient distribution of the LUTa, an addressregion where the distortion compensation coefficient is clipped to theupper limit of the coefficient setting range occurs, and with thedistortion compensation coefficient distribution of the LUTb, an addressregion where the distortion compensation coefficient is clipped to thelower limit of the coefficient setting range occurs. An address regionwhere the distortion compensation coefficient is clipped fails toexpress the distortion compensation coefficient to be originally set,and consequently, the distortion compensation performance deteriorates.

Also, with the multiplier 120 as well, distortion compensationprocessing as to the transmission signal Tx(t) is performed using thepost-synthesis coefficient h2(p(t)) to be obtained by adding thedistortion compensation coefficient hc(p(t)) output from the LUTc andthe distortion compensation coefficient hd(p(t−1)) output from the LUTd.Accordingly, with the LUTc and LUTd as well, in the same way as with theLUTa and LUTb, a problem occurs wherein the distortion compensationperformance deteriorates.

1. First Embodiment

Description will be made regarding a wireless communication device and adistortion compensation apparatus according to a first embodiment.

1-1. Configuration Example of Wireless Communication Apparatus 300

FIG. 3 is a diagram illustrating an example of the configuration of awireless communication device 300 including a multi-LUT-type distortioncompensation apparatus 302. As illustrated in FIG. 3, the wirelesscommunication device 300 includes a distortion compensation apparatus302, a digital/analog converter (DAC) 304, an up converter 306, areference carrier wave generator 308, a power amplifier 310, a downconverter 312, a reference carrier wave generator 314, and ananalog/digital converter (ADC) 316.

The distortion compensation apparatus 302 is a multi-LUT-type distortioncompensation apparatus, and includes a pre-distortion signal generatingunit 322, and a distortion compensation coefficient updating unit 324.The pre-distortion signal generating unit 322 includes multiple LUT, andreceives a transmission signal Tx(t) from a transmission signalgenerating device not illustrated. The pre-distortion signal generatingunit 322 synthesizes multiple distortion compensation coefficientsstored in the multiple LUT, thereby generating a post-synthesiscoefficient, and generating a pre-distortion signal PD(t) based on thereceived transmission signal Tx(t) and the generated post-synthesiscoefficient. The details of the pre-distortion signal generating unit322 will be described later.

The pre-distortion signal PD(t) is converted into an analog signal bythe DAC 304. The up converter 306 receives the converted pre-distortionsignal, performs orthogonal modulation using the reference carrier wavessupplied from the reference carrier wave generator 308, and alsoperforms frequency conversion into a wireless frequency. The poweramplifier 310 receives the pre-distortion signal subjected to theorthogonal modulation and frequency conversion, performs poweramplification of the received pre-distortion signal, and generates awireless transmission signal. The power amplifier 310 transmits thewireless transmission signal in the air via an antenna not illustratedby radio, and also feeds back the wireless transmission signal to thedown converter 312.

The down converter 312 receives the wireless transmission signal fedback, performs orthogonal detection using the reference carrier wavegenerator 314, and also performs frequency conversion into the originalbaseband frequency. The signal subjected to the orthogonal detection andfrequency conversion is converted into a digital signal by the ADC 316,and supplied to the distortion compensation coefficient updating unit324 as a feedback signal Fb(t).

The distortion compensation coefficient updating unit 324 receives thefeedback signal Fb(t), and also receives the pre-distortion signal PD(t)from the pre-distortion signal generating unit 322. Also, the distortioncompensation coefficient updating unit 324 receives a distortioncompensation coefficient h(p) from the multiple LUT within thepre-distortion signal generating unit 322. The distortion compensationcoefficient updating unit 324 performs adaptive signal processing usingLMS (Least Mean Square) algorithm for example, thereby updating thevalue of the distortion compensation coefficient stored in each of themultiple LUT included in the pre-distortion signal generating unit 322.

The distortion compensation coefficient updating unit 324 subjects thefeedback signal Fb(t) to the same distortion compensation processing aswith the transmission signal Tx(t), thereby generating a referencepre-distortion signal PDref(t). The distortion compensation coefficientupdating unit 324 calculates the updated value of the receiveddistortion compensation coefficient h(p) as to each LUT using theadaptive signal processing employing the LMS algorithm so as to obtainzero as difference between the received pre-distortion signal PD(t) andthe generated reference pre-distortion signal PDref(t). The distortioncompensation coefficient updating unit 324 updates the value of thedistortion compensation coefficient within each LUT in a mannercorrelated with the power value of the corresponding transmission signalbased on the calculated updated value. The distortion compensationcoefficient updating unit 324 repeatedly executes the above distortioncompensation coefficient updating processing, thereby operating so as tohave the value of the distortion compensation coefficient within eachLUT converge into a certain value corresponding to each power value ofthe transmission signals. Note that, with regard to distortioncompensation coefficient updating processing to be executed at thedistortion compensation coefficient updating unit 324, processingdescribed in the Specific and drawings of a prior application (JapanesePatent Application No. 2010-236432) by the present patent applicant canbe employed.

Note that the distortion compensation apparatus 302 can be realized witha digital signal processing device such as FPGA, ASIC, or the like, or aprocessor such as a DSP or the like, for example. Also, the distortioncompensation apparatus 302 may be realized as a single device, or may berealized as a combination of multiple devices each having a part of thefunction of the distortion compensation apparatus 302. Also, therespective LUT included in the distortion compensation apparatus 302 maybe realized with a storage device such as independent RAM or the like.

1-2. Configuration Example of Pre-Distortion Signal Generating Unit 322

FIG. 4 is a diagram illustrating an example of the internalconfiguration of the pre-distortion signal generating unit 322. FIG. 5is a diagram for describing distortion compensation coefficientcorrection processing at the pre-distortion signal generating unit 322.Hereafter, description will be made regarding a configuration example ofthe pre-distortion signal generating unit 322 using FIGS. 4 and 5.

As illustrated in FIG. 4, the pre-distortion signal generating unit 322includes a distortion compensation coefficient supplying unit 450, adistortion compensation processing unit 460, and an offset correctionprocessing unit 470.

The distortion compensation coefficient supplying unit 450 includes anaddress generating unit 402, a delay unit 404, a LUTa (look up table)406, a LUTb 408, a LUTc 410, and a LUTd 412. The distortion compensationprocessing unit 460 includes adders 414 and 416, multipliers 418 and420, and a delay unit 422, and an adder 424.

The look up tables LUTa 406 through LUTd 412 are distortion compensationcoefficient storage units which store a distortion compensationcoefficient, and are RAM, for example. The LUTa 406 through LUTd 412store multiple distortion compensation coefficients ha(p(t)) throughhd(p(t)) in an address correlated with the power value p(t) of thetransmission signal Tx(t) respectively. Each LUT correlates the addressof each LUT with the power value p(t) of the transmission signal Tx(t)in a one-on-one manner, for example, and the higher the power value p(t)of the transmission signal Tx(t) is, stores the corresponding distortioncompensation coefficient h(p(t)) in an address having a greater value.

The offset correction processing unit 470 includes an offset controlunit 432, compensation value storage units 436 and 440, and offsetcompensation units 438 and 442. The offset control unit 432 includes amean value calculating unit 434.

With the offset correction processing unit 470, the offset control unit432 individually executes the following offset amount calculationprocessing and offset correction processing regarding each of the LUTa406 through LUTd 412.

The offset control unit 432 selects a LUT to be processed out of theLUTa 406 through LUTd 412. At the selected LUT for processing, theoffset control unit 432 reads out all of the distortion compensationcoefficients h(p_(i)) from an address A_(i) within the region of anaddress where the distortion compensation coefficient to be corrected isstored.

As illustrated in FIG. 5, the mean value calculating unit 434 performsaddition averaging operation indicated with the following Expression 1regarding all of the read distortion compensation coefficients h(p_(i))to calculate a mean value. The offset control unit 432 calculates themean value of the distortion compensation coefficients using the meanvalue calculating unit 434, thereby performing calculation processing ofoffset amount LUTofst_x (x is any of a through d) of the distortioncompensation coefficient as to a LUT_x to be processed.

$\begin{matrix}{{LUTofst\_ x} = \frac{\sum\limits_{A_{i} = {adrsMin}}^{adrsMax}{h\left( p_{i} \right)}}{N}} & \left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, with Expression 1, LUTofst_x is the offset amount of thedistortion compensation coefficient within the LUT_x, adrsMax is themaximum value of the address to be corrected, adrsMin is the minimumvalue of the address to be corrected, h(p_(i)) is a distortioncompensation coefficient stored in the address A_(i) of the LUT_x, and Nis the number of addresses from the address minimum value adrsMin tomaximum value adrsMax to be corrected.

Note that the distortion compensation coefficient h(p(t)) is expressedwith a complex number, and accordingly, the above-mentioned offsetamount calculation processing is individually executed as to each of thereal portion (I-channel component) and imaginary portion (Q-channelcomponent) of a distortion compensation coefficient. Also, this cansimilarly be applied to later-described processing such as offsetcorrection value setting processing, offset correction processing,offset compensation value updating processing, offset compensationprocessing, and so forth, and processing such as distortion compensationprocessing, distortion compensation coefficient updating processing, andso forth.

The offset control unit 432 performs the setting processing of theoffset correction value Ofst_x as to the LUT_x to be processed based onthe calculated offset amount LUTofst_x. The offset control unit 432changes the offset correction value Ofst_x to a different valueaccording to whether the calculated offset amount LUTofst_x is apositive value or negative value. The details of the offset correctionvalue setting processing will be described later.

The offset control unit 432 performs offset correction processing as toall of the distortion compensation coefficients stored within theaddress region to be corrected based on the set offset correction valueOfst_x at the LUT_x to be processed. The offset control unit 432performs, as illustrated in FIG. 5 for example, the correctionprocessing of the offset of each distortion compensation coefficientbased on the set offset correction value Ofst_x so as reduce themagnitude (absolute value) of the offset amount of each distortioncompensation coefficient stored in the LUT to be processed. The offsetcontrol unit 432 writes the distortion compensation coefficientsubjected to the offset compensation processing in the addresscorresponding to the LUT_x to be processed, thereby correcting theoffset of the distortion compensation coefficient within the LUT to beprocessed. The details of the offset correction processing will bedescribed later.

According to repeating the above-mentioned processing regarding the LUTa406 through LUTd 412, the offset control unit 432 calculates offsetamount LUTofst_a through offset amount LUTofst_d as to the LUTa 406through LUTd 412, performs processing for setting offset correctionvalues Ofst_a through Ofst_d, and also performs the offset correctionprocessing as to each of the LUTa 406 through LUTd 412.

The offset control unit 432 performs updating processing of the offsetcompensation values within the compensation value storage unit 436 basedon the calculated offset amount LUTofst_a and offset amount LUTofst_b.The offset control unit 432 calculates the updated value of an offsetcompensation value Ofst_m1 based on the offset amount LUTofst_a andoffset amount LUTofst_b, and stores the calculated updated value of theoffset compensation value Ofst_m1 in the compensation value storage unit436. The offset compensation value Ofst_m1 corresponds to a valueobtained by accumulatively adding a difference value (offset correctionvalue) between distortion compensation coefficients before and after theabove offset correction processing at the LUTa 406, and a differencevalue (offset correction value) between distortion compensationcoefficients before and after the above offset correction processing atthe LUTb 408. The details of the updating processing of an offsetcompensation value will be described later.

Similarly, the offset control unit 432 performs updating processing ofthe offset compensation values within the compensation value storageunit 440 based on the calculated offset amount LUTofst_c and offsetamount LUTofst_d. The offset control unit 432 calculates the updatedvalue of an offset compensation value Ofst_m2 based on the offset amountLUTofst_c and offset amount LUTofst_d, and stores the calculated updatedvalue of the offset compensation value Ofst_m2 in the compensation valuestorage unit 440. The offset compensation value Ofst_m2 corresponds to avalue obtained by accumulatively adding a difference value (offsetcorrection value) between distortion compensation coefficients beforeand after the above offset correction processing at the LUTc 410, and adifference value (offset correction value) between distortioncompensation coefficients before and after the above offset correctionprocessing at the LUTd 412.

With the distortion compensation coefficient supplying unit 450, theaddress generating unit 402 receives the transmission signal Tx(t),generates an address Adrs(Tx(t)) corresponding to the power value p(t)of the transmission signal Tx(t). For example, the address generatingunit 402 correlates the power value p(t) of the transmission signalTx(t) with the address Adrs(Tx(t)) in a one-on-one manner, and thehigher the power value p(t) of the transmission signal Tx(t) is,generates an address Adrs(Tx(t)) having a greater value. The generatedaddress Adrs(Tx(t)) is supplied to the LUTa 406 and LUTc 410.

The delay unit 404 receives the address Adrs(Tx(t)) generated by theaddress generating unit 402. The delay unit 404 outputs the receivedaddress Adrs(Tx(t)) by delaying the output of the received addressAdrs(Tx(t)) by time equivalent to the previous reference point-in-time,thereby generating an address Adrs(Tx(t−1)) corresponding to the powervalue p(t−1) of the transmission signal Tx(t−1) at the previousreference point-in-time t−1. The generated address Adrs(Tx(t−1)) issupplied to the LUTb 408 and LUTd 412.

The LUTa 406 receives the address Adrs(Tx(t)), and reads out thecorresponding distortion compensation coefficient ha(p(t)) output fromthe received address Adrs(Tx(t)). The LUTa 406 outputs the readdistortion compensation coefficient ha(p(t)) to the adder 414. Thedistortion compensation coefficient ha(p(t)) from the LUTa 406 is adistortion compensation coefficient after the offset correctionprocessing by the offset control unit 432. Also, similarly, the LUTc 410receives the address Adrs(Tx(t)), and outputs the correspondingdistortion compensation coefficient hc(p(t)) to the adder 416. Thedistortion compensation coefficient hc(p(t)) output from the LUTc 410 isa distortion compensation coefficient after the offset correctionprocessing.

The LUTb 408 receives the address Adrs(Tx(t−1)), and reads out thecorresponding distortion compensation coefficient hb(p(t−1)) from thereceived address Adrs(Tx(t−1)). The LUTb 408 outputs the read distortioncompensation coefficient hb(p(t−1)) to the adder 414. The distortioncompensation coefficient hb(p(t)) output from the LUTb 408 is adistortion compensation coefficient after the offset correctionprocessing by the offset control unit 432. Also, similarly, the LUTd 412receives the address Adrs(Tx(t−1)), and outputs the correspondingdistortion compensation coefficient hd(p(t−1)) to the adder 416. Thedistortion compensation coefficient hd(p(t)) output from the LUTd 412 isa distortion compensation coefficient after the offset correctionprocessing.

With the distortion compensation processing unit 460, the adder 414receives the distortion compensation coefficients ha(p(t)) andhb(p(t−1)) from the LUTa 406 and LUTb 408. The adder 414 performssynthesis by adding the distortion compensation coefficients ha(p(t))and hb(p(t−1)) to generate a post-synthesis coefficient h1(p(t)). Theadder 414 outputs the post-synthesis coefficient h1(p(t)) to the offsetcompensation unit 438.h1(p(t))=ha(p(t))+hb(p(t−1))

Similarly, the adder 416 receives the distortion compensationcoefficients hc(p(t)) and hd(p(t−1)) from the LUTc 410 and LUTd 412. Theadder 416 performs synthesis by adding the distortion compensationcoefficients hc(p(t)) and hd(p(t−1)) to generate a post-synthesiscoefficient h2(p(t)). The adder 416 outputs the post-synthesiscoefficient h2(p(t)) to the offset compensation unit 442.h2(p(t))=hc(p(t))+hd(p(t−1))

The offset compensation unit 438 receives the post-synthesis coefficienth1(p(t)) from the adder 414, and also receives the offset compensationvalue Ofst_m1 from the compensation value storage unit 436. The offsetcompensation unit 438 adds the offset compensation value Ofst_m1 to thereceived post-synthesis coefficient h1(p(t)), thereby performing offsetcompensation processing as to the post-synthesis coefficient h1(p(t)) togenerate a post-offset-compensation coefficient h3(p(t)).h3(p(t))=h1(p(t))+Ofst_(—) m1

The offset compensation unit 438 outputs the generatedpost-offset-compensation coefficient h3(p(t)) to the multiplier 418. Thepost-offset-compensation coefficient h3(p(t)) corresponds to a valueobtained by adding the distortion compensation coefficient in the casethat the offset correction processing by the offset control unit 432 hasnot been performed at the LUTa 406, and the distortion compensationcoefficient in the case that the offset correction processing has notbeen performed at the LUTb 408, and is an additional value in the casethat the offset correction processing has not been performed using theoffset compensation value Ofst_m1 generated in a pseudo manner.

The offset compensation unit 442 receives the post-synthesis coefficienth2(p(t)) from the adder 416, and also receives the offset compensationvalue Ofst_m2 from the compensation value storage unit 440. The offsetcompensation unit 442 adds the offset compensation value Ofst_m2 to thereceived post-synthesis coefficient h2(p(t)), thereby performing offsetcompensation processing as to the post-synthesis coefficient h2(p(t)) togenerate a post-offset-compensation coefficient h4(p(t)).h4(p(t))=h2(p(t))+Ofst_(—) m2

The offset compensation unit 442 outputs the generatedpost-offset-compensation coefficient h4(p(t)) to the multiplier 420. Thepost-offset-compensation coefficient h4(p(t)) corresponds to a valueobtained by adding the distortion compensation coefficient in the casethat the offset correction processing by the offset control unit 432 hasnot been performed at the LUTc 410, and the distortion compensationcoefficient in the case that the offset correction processing has notbeen performed at the LUTd 412, and is an additional value in the casethat the offset correction processing has not been performed using theoffset compensation value Ofst_m2 generated in a pseudo manner.

The multiplier 418 receives the transmission signal Tx(t), and alsoreceives the post-offset-compensation coefficient h3(p(t)) from theoffset compensation unit 438. The multiplier 418 multiplies thetransmission signal Tx(t) and post-offset-compensation coefficienth3(p(t)) to generate a transmission signal Tx1(t). The multiplier 418outputs the generated transmission signal Tx1(t) to the adder 424.Tx1(t)=Tx(t)×h3(p(t))

The delay unit 422 outputs the transmission signal Tx(t) by delaying theoutput of the transmission signal Tx(t) by time equivalent to theprevious reference point-in-time, thereby generating a transmissionsignal Tx(t−1)) at the previous reference point-in-time t−1. The delayunit 422 outputs the generated transmission signal Tx(t−1) to themultiplier 420.

The multiplier 420 receives the transmission signal Tx(t−1) from thedelay unit 422, and also receives the post-offset-compensationcoefficient h4(p(t)) from the offset compensation unit 442. Themultiplier 420 multiplies the transmission signal Tx(t−1) andpost-offset-compensation coefficient h4(p(t)) to generate a transmissionsignal Tx2(t−1). The multiplier 420 outputs the generated transmissionsignal Tx2(t−1) to the adder 424.Tx2(t−1)=Tx(t−1)×h4(p(t))

The adder 424 adds the transmission signals Tx1(t) and Tx2(t−1), therebygenerating a pre-distortion signal PD(t). The pre-distortion signalPD(t) is a transmission signal after the transmission signal Tx(t) inputto the distortion compensation apparatus 302 is subjected to distortioncompensation processing.PD(t)=Tx1(t)+Tx2(t−1)

As described above, with the multi-LUT-type distortion compensationapparatus 302, a delay term is generated by the delay units 404 and 422as to the transmission signal Tx(t), thereby reflecting the informationof the transmission signal Tx(t−1) at the previous referencepoint-in-time t−1 on the distortion compensation processing as to thetransmission signal Tx(t), and accordingly, distortion due to memoryeffect of the power amplifier can be compensated in addition tononlinear distortion of the power amplifier.

Also, with the pre-distortion signal generating unit 322 of thedistortion compensation apparatus 302, the offset amount of thedistortion compensation coefficient is calculated at each of the look uptables LUTa 406 through LUTd 412, and the offset correction processingof each distortion compensation coefficient based on the calculatedoffset amount so as to reduce the offset amount of the distortioncompensation coefficient. Accordingly, at each LUT, even in the event ofupdating of the distortion compensation coefficient advancing, theoffset of the distortion compensation coefficient monotonously increasesor decreases in one direction. As a result thereof, the distortioncompensation coefficient can be suppressed from being clipped to theupper limit or lower limit of the coefficient setting range.Accordingly, with the distortion compensation apparatus 302, thedistortion compensation performance can be suppressed fromdeteriorating.

Further, with the distortion compensation apparatus 302, according tothe offset compensation units 438 and 442, a distortion compensationcoefficient in the case that the offset correction processing at eachLUT has not been performed is generated in a pseudo manner, and thedistortion compensation processing of the transmission signal Tx(t) isperformed based on the distortion compensation coefficient before theoffset correction processing generated in a pseudo manner. Thus, withthe distortion compensation apparatus 302, even in the event that thevalue of the distortion compensation coefficient stored in each LUT hasbeen corrected by the offset correction processing, suitable distortioncompensation processing can be performed using the distortioncompensation coefficient generated in a pseudo manner, and the precisionof the distortion compensation processing can be maintained.

1-3. Example of Correction and Updating Operation of DistortionCompensation Coefficient at Distortion Compensation Apparatus 302

FIG. 6 is a diagram illustrating an example of a flowchart of distortioncompensation coefficient correction and updating processing at thedistortion compensation apparatus 302. Hereafter, description will bemade regarding the distortion compensation coefficient correction andupdating processing that the distortion compensation apparatus 302executes, using the flowchart in FIG. 6. Note that, with the flowchartin FIG. 6, a numeric expression relating to the processing of thecorresponding step is indicated in a portion surrounded by a dottedline.

First, in step S602, the distortion compensation apparatus 302 startscorrection and updating processing of a series of distortioncompensation coefficients.

Next, in step S604, the offset control unit 432 of the offset correctionprocessing unit 470 sets parameters used for later-described offsetcorrection value setting processing 660, offset compensation valueupdating processing 670, and offset correction processing 680 as initialsetting. Examples of the parameters to be set include the offsetcorrection unit Ofst_u to be used for the offset correction valuesetting processing, the address minimum value adrsMin and maximum valueadrsMax within each LUT where a distortion compensation coefficient tobe corrected in the offset correction processing is stored, and offsetcompensation values Ofst_m1 and Ofst_m2 to be stored in the compensationvalue storage units 436 and 440 in the offset compensation valueupdating processing.

Though not particularly restricted, a certain positive value u_(o) isset as the offset correction unit Ofst_u, and 0 (zero) is set as theoffset compensation values Ofst_m1 and Ofst_m2.Ofst_(—) u=u _(o)Ofst_(—) m1=0, Ofst_(—) m2=0

Also, though not particularly be restricted, the minimum value A_(min)and maximum value A_(max) of addresses where a correction coefficient isstored in the respective LUT are set as the address minimum valueadrsMin and maximum value adrsMax to be corrected, respectively.adrsMin=A _(min)adrsMax=A _(max)

Next, in step S606, the offset control unit 431 selects one LUT to beprocessed out of the LUTa 406 through LUTd 412. The offset control unit432 cyclically selects the corresponding LUT in the sequence of LUTa406, LUTb 408, LUTc 410, LUTd 412, LUTa 406, LUTb 408, and so on, forexample.

Next, in step S608, the offset control unit 432 reads out the distortioncompensation coefficient h(p_(i)) from the LUT to be processed selectedin step S606. At this time, the offset control unit 432 reads out thedistortion compensation coefficient h(p_(i)) from all of the addressesin a range from the address minimum value adrsMin to maximum valueadrsMax.

Next, in step S610, the offset control unit 432 performs the additionaveraging operation indicated in the above Expression 1 regarding all ofthe distortion compensation coefficient h(p(t)) read out in step S608.According to this addition averaging operation, the offset control unit432 performs processing for calculating the offset amount LUTofst_x ofthe distortion compensation coefficient as to the LUTx to be processed(x is any of a through d).

Note that the distortion compensation coefficient h(p) is expressed witha complex number, and accordingly, the above-mentioned offset amountcalculation processing is individually executed as to each of the realportion (I-channel component) and imaginary portion (Q-channelcomponent) of a distortion compensation coefficient. Also, this cansimilarly be applied to later-described processing such as offsetcorrection value setting processing, offset correction processing,offset compensation value updating processing, and so forth, which willbe executed in later-described steps.

Next, in step S612, the offset control unit 432 determines whether thecalculated offset amount LUTofst_x is 0 (zero), a positive value, or anegative value.

When determining that the offset amount LUTofst_x is a positive value(LUTofst_x>0), the offset control unit 432 performs processing forsetting the offset correction value Ofst_x as to the LUTx to beprocessed using the offset correction unit Ofst_u as follows.Specifically, the offset control unit 432 sets the certain positivevalue u_(o) as the offset correction value.Ofst_(—) x=+Ofst_(—) u=+u _(o)

When determining that the offset amount LUTofst_x is a negative value(LUTofst_x<0), the offset control unit 432 performs processing forsetting the offset correction value Ofst_x as to the LUTx to beprocessed using the offset correction unit Ofst_u as follows.Specifically, the offset control unit 432 sets the certain negativevalue u_(o) as the offset correction value.Ofst_(—) x=−Ofst_(—) u=−u _(o)

When determining that the offset amount LUTofst_x is 0 (zero)(LUTofst_x=0), the offset control unit 432 performs processing forsetting the offset correction value Ofst_x as to the LUTx to beprocessed as follows. Specifically, the offset control unit 432 sets theoffset correction value to 0 (zero).Ofst_(—) x=0

According to the above steps S608 through S612, the offset amountcalculation processing 650 and offset correction value settingprocessing 660 are performed at the offset correction processing unit470.

Next, in step S614, the offset control unit 432 reads out the offsetcorrection values Ofst_m1 and Ofst_m2 from the compensation valuestorage unit 436 or 440, and sets the read offset correction value asthe updated value Ofst_m of the offset correction value.

Here, in the event that the LUT to be processed selected in step S606 isthe LUTa or LUTb, the offset control unit 432 reads out the offsetcompensation value Ofst_m1 stored in the compensation value storage unit436, and sets the read offset compensation value Ofst_m1 as the updatedvalue Ofst_m.Ofst_(—) m=Ofst_(—) m1

Also, in the event that the selected LUT to be processed is the LUTc orLUTd, the offset control unit 432 reads out the offset compensationvalue Ofst_m2 stored in the compensation value storage unit 440, andsets the read offset compensation value Ofst_m2 as the updated valueOfst_m.Ofst_(—) m=Ofst_(—) m2

Next, in step S616, the offset control unit 432 adds the offsetcorrection value Ofst_x set in step S612 to the updated value Ofst_m setin step S614, and calculates the additional value as a new updated valueOfst_m.Ofst_(—) m=Ofst_(—) m+Ofst_(—) x

Next, in step S618, the offset control unit 432 stores the updated valueOfst_m of the offset compensation value calculated in step S616 in thecompensation value storage unit 436 or 440, and updates the offsetcompensation value Ofst_m1 or Ofst_m2 within the compensation valuestorage unit 436 or 440.

Here, in the event that the LUT to be processed selected in step S606 isthe LUTa or LUTb, the offset control unit 432 stores the updated valueOfst_m of the offset compensation value in the compensation valuestorage unit 436, and updates the offset compensation value Ofst_m1within the compensation value storage unit 436.

Also, in the event that the LUT to be processed selected in step S606 isthe LUTc or LUTd, the offset control unit 432 stores the updated valueOfst_m of the offset compensation value in the compensation valuestorage unit 440, and updates the offset compensation value Ofst_m2within the compensation value storage unit 440.

According to the above steps S614 through S618, the offset compensationvalue updating processing 670 is performed at the offset correctionprocessing unit 470.

Next, in step S620, the offset control unit 432 specifies the addressminimum value adrsMin to be corrected (=A_(min)) set in step S604 to thevalue of the address A_(i) to be accessed within the LUT to be processedselected in step S606. An address to be accessed within the LUT to beprocessed corresponds to the address where the distortion compensationcoefficient to be subjected to the offset correction processing isstored.A _(i)=adrsMin=A _(min)

Next, in step S622, the offset control unit 432 determines whether ornot the value of the specified address A_(i) to be accessed is equal toor smaller than the address maximum value adrsMax to be corrected set instep S604. In the event that the specified address A_(i) to be accessedis equal to or smaller than the maximum value adrsMax, the processingproceeds to step S624. In the event that the specified address isgreater than the maximum value adrsMax, the processing proceeds to stepS628.

Next, in step S624, the offset control unit 432 reads out thecorresponding distortion compensation coefficient h(p_(i)) from theaddress A_(i) to be accessed, specified within the LUT to be processed.The offset control unit 432 subtracts the offset correction value Ofst_xset in step S612 from the read distortion compensation coefficienth(p_(i)) to calculate the subtraction value as the value of thedistortion compensation coefficient h(p_(i)) after correction. Theoffset control unit 432 writes the calculated distortion compensationcoefficient h(p_(i)) after correction in the address A_(i) to beaccessed and processed, thereby correcting the distortion compensationcoefficient h(p_(i)).h(p _(i))=h(p _(i))−Ofst_(—) x

Next, in step S626, the offset control unit 432 increments the value ofthe address A_(i) within the LUT to be processed by one for example,thereby specifying the value of an address that has a greater value nextto the current address, and can be specified as an address value to beaccessed, as the value of the next address to be accessed within the LUTto be processed. After the value of the next address A_(i) is specified,the processing returns to step S622.A _(i) =A _(i)+1

Next, in step S628, the offset control unit 432 stores the distortioncompensation coefficient h(p_(i)) after correction calculated in stepS624 in the address A_(i) of the LUT to be processed regarding all ofthe addresses in a range from the address minimum value adrsMin to themaximum adrsMax, and corrects the value of the distortion compensationcoefficient in the address A_(i). Thus, all of the distortioncompensation coefficients to be corrected within the LUT to be processedare subjected to the offset correction processing.

According to the above steps S620 through S628, the offset correctionprocessing 680 is performed at the offset correction processing unit470.

A series of processing performed by the above steps S604 through S628 isdistortion compensation coefficient correction processing that thedistortion compensation apparatus 302 executes.

Next, in step S630, the distortion compensation coefficient updatingunit 324 receives the distortion compensation coefficient h(p(t)) fromthe multiple LUT within the pre-distortion signal generating unit 322.The distortion compensation coefficient that the distortion compensationcoefficient updating unit 324 receives is a coefficient subjected to theoffset correction processing 680. The distortion compensationcoefficient updating unit 324 further receives a feedback signal Fb(t)from the ADC 316, and also receives the pre-distortion signal PD(t) fromthe pre-distortion signal generating unit 322. The pre-distortion signalPD(t) is a signal generated based on a distortion compensationcoefficient subjected to the offset compensation processing using theoffset compensation value updated by the offset compensation valueupdating processing 670.

In step S630, the distortion compensation coefficient updating unit 324calculates the updated value of the distortion compensation coefficientas to each LUT based on the received distortion compensation coefficienth(p(t)), pre-distortion signal PD(t), and feedback signal Fb(t).Calculation of the updated value of the distortion compensationcoefficient is as described above. With an address within each LUT wherethe received distortion compensation coefficient is stored, based on thecalculated updated value, the distortion compensation coefficientupdating unit 324 updates the value of the distortion compensationcoefficient. After the distortion compensation coefficient updatingprocessing, the processing returns to step S606.

In step S606, the offset control unit 432 selects another LUT out of theLUTa 406 through LUTd 412 as the next LUT to be processed. The offsetcontrol unit 432 performs the processing in the above steps S608 throughS628 regarding the selected LUT to be processed to perform the offsetamount calculation processing 650, offset correction value settingprocessing 660, offset compensation value updating processing 670, andoffset correction processing 680 respectively.

As described above, with the distortion compensation coefficientcorrection and updating processing illustrated in FIG. 6, the offsetamount of the distortion compensation coefficient at each of the LUTa406 through LUTd 412 can be calculated by the offset amount calculationprocessing 650, and the value of each distortion compensationcoefficient can be corrected by the offset correction processing 680based on the calculated offset amount so as to reduce the magnitude(absolute value) of the offset amount thereof.

Thus, even in the event that the distortion compensation coefficientupdating processing has advanced at each LUT, the offset of thedistortion compensation coefficient can be suppressed from monotonouslyincreasing or decreasing in one direction, and accordingly, thedistortion compensation performance can be suppressed by clipping thedistortion compensation coefficient to the upper limit or lower limit inthe coefficient setting range.

Further, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 6, according to the offsetcompensation value updating processing 670, offset compensation valuescorresponding to the additional value of the distortion compensationcoefficients from the LUTa and LUTb (the output value of the adder 414),and the additional value of the distortion compensation coefficientsfrom the LUTc and LUTd (the output value of the adder 416) can besuitable set. Thus, a distortion compensation coefficient in the eventthat the offset correction processing at each LUT has not been performedis generated in a pseudo manner, and the distortion compensationprocessing of a transmission signal can be performed based on thedistortion compensation coefficient generated in a pseudo manner beforethe offset correction processing.

Accordingly, even in the event that the value of the distortioncompensation coefficient stored in each LUT has been corrected by theoffset correction processing 680, suitable distortion compensationprocessing can be performed using the distortion compensationcoefficient generated in a pseudo manner, and accordingly, the precisionof the distortion compensation processing can be maintained.

Further, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 6, according to the offsetcorrection value setting processing 660, a suitable value according tothe offset amount calculated by the offset amount calculation processing650 can be set as the offset correction value as to the distortioncompensation coefficient within each LUT. Thus, the offset amount of thedistortion compensation coefficient can be suitably controlled at eachLUT so as to reduce the magnitude (absolute value) thereof.

Also, with the offset correction processing unit 680, the offset of thedistortion compensation coefficient within each LUT is correctedindependently from the distortion compensation coefficient updatingprocessing at the distortion compensation coefficient updating unit 324,and accordingly, this can be conceived to affect convergence of adistortion compensation coefficient in the updating processing. However,with the distortion compensation coefficient correction and updatingprocessing illustrated in FIG. 6, the value of the offset correctionunit Ofst_u used for the offset correction value setting processing 660is suitably adjusted, whereby the offset correction processing 680 cansuppress influence to be applied to the convergence of a distortioncompensation coefficient small in the distortion compensationcoefficient updating processing.

Accordingly, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 6, the distortion compensationperformance can be suppressed from deterioration due to clipping of adistortion compensation coefficient while maintaining the precision ofthe distortion compensation processing.

Note that, with the above embodiment, an arrangement has been madewherein the delay units are provided to the transmission signal Tx(t)and address Adrs(Tx(t)) one at a step, and one delay term is provided toeach, but the present disclosure is not restricted to this. Anarrangement may be made wherein delay units are provided to thetransmission signal Tx(t) and address Adrs(Tx(t)) i steps and j stepsrespectively, and i delay terms and j delay terms are provided theretorespectively (however, i and j are integers equal to one or greater thanone).

2. Second Embodiment

Hereafter, description will be made regarding a wireless communicationdevice and a distortion compensation apparatus, according to a secondembodiment.

2-1. Configuration Example of Pre-Distortion Signal Generating Unit 722

Though the configuration of a wireless communication device 700according to the second embodiment differs from the configuration of thewireless communication device 300 illustrated in FIG. 3 in that adistortion compensation apparatus 702 and a pre-distortion signalgenerating unit 722 are provided instead of the distortion compensationapparatus 302 and pre-distortion signal generating unit 322, portionsother than those are the same. Accordingly, with regard to theconfiguration of the wireless communication apparatus 700, drawingthereof is omitted.

FIG. 7 is a diagram illustrating an example of the internalconfiguration of the pre-distortion signal generating unit 722. Thoughthe internal configuration of the pre-distortion signal generating unit722 differs from the internal configuration of the pre-distortion signalgenerating unit 322 illustrated in FIG. 4 in that an offset control unit732 and an offset correction processing unit 770 are provided instead ofthe offset control unit 432 and offset correction processing unit 470,portions other than those are the same. In FIG. 7, the same orcorresponding portions are denoted with the same reference numerals aswith the pre-distortion signal generating unit 322 illustrated in FIG.4.

As illustrated in FIG. 7, the pre-distortion signal generating unit 722includes a distortion compensation coefficient supplying unit 450, adistortion compensation processing unit 460, and an offset correctionprocessing unit 770. The offset correction processing unit 770 includesan offset control unit 732, compensation value storage units 436 and440, and offset compensation units 438 and 442. The offset control unit732 includes a mean value calculating unit 434 in the same way as withthe offset control unit 432.

With the offset correction processing unit 770, the offset control unit732 executes the following offset amount calculation processing, offsetamount determination processing, and offset correction processingindividually regarding each of the LUTa 406 through LUTd 412.

The offset control unit 732 selects a LUT to be processed out of theLUTa 406 through LUTd 412. The offset control unit 432 reads out thedistortion compensation coefficient h(p_(i)) from all of the addressesA_(i) where a distortion compensation coefficient to be corrected isstored, within the LUT selected to be processed.

The mean value calculating unit 434 of the offset control unit 732performs the addition averaging operation indicated with the aboveExpression 1 regarding all of the read distortion compensationcoefficients h(p_(i)). The offset control unit 732 calculates a meanvalue using the mean value calculating unit 434, thereby performing thecalculation processing of the offset amount LUTofst of the distortioncompensation coefficients as to the LUT to be processed.

The offset control unit 732 performs determination processing of theoffset amount LUTofst prior to the offset correction value settingprocessing by determining whether or not the calculated offset amountLUTofst of the distortion compensation coefficients is a value within apredetermined range.

When determining that the calculated offset amount LUTofst is a valuewithin a predetermined range, the offset control unit 732 does notperform the offset correction processing as to the distortioncompensation coefficients of the LUT to be processed. On the other hand,when determining that the calculated offset amount LUTofst is a valueout of a predetermined range (is not a value within a predeterminedrange), the offset control unit 732 executes the offset correctionprocessing as to the distortion compensation coefficients of the LUT tobe processed.

Accordingly, with the distortion compensation apparatus 702, the offsetcontrol unit 732 can be controlled so that when the magnitude (absolutevalue) of the calculated offset amount is smaller than a certainthreshold, and necessity to perform offset correction processing of thedistortion compensation coefficient at each LUT is low, the offsetcorrection processing is not performed, and when the magnitude (absolutevalue) of the calculated offset amount is greater than a certainthreshold, and necessity to perform offset correction processing of thedistortion compensation coefficient at each LUT is high, the offsetcorrection processing is selectively executed, and accordingly, theoffset correction processing can more effectively be performed at theoffset control unit 732.

Accordingly, with the distortion compensation apparatus 702, the powerconsumption of the offset correction processing unit 770 and distortioncompensation coefficient supplying unit 450 can be reduced.

2-2. Example of Distortion Compensation Coefficient Correction andUpdating Operation at Distortion Compensation Apparatus 702

FIG. 8 is a diagram illustrating an example of a flowchart of distortioncompensation coefficient correction and updating processing at thedistortion compensation apparatus 702 according to the secondembodiment. With the flowchart of the distortion compensationcoefficient correction and updating processing illustrated in FIG. 8,the same or corresponding steps are denoted with the same referencenumerals as with the steps of the flowchart illustrated in FIG. 6.Hereafter, description will be made regarding the distortioncompensation coefficient correction and updating processing that thedistortion compensation apparatus 702 executes, with reference to theflowchart in FIG. 8. Note that, with the flowchart in FIG. 8, a numericexpression relating to the processing in the corresponding step isindicated in a portion surrounded with a dotted line.

First, in step S602, the distortion compensation apparatus 702 starts aseries of the distortion compensation coefficient correction andupdating processing.

Next, in step S804, the offset control unit 732 sets parameters used forlater-described offset amount determination processing 855 and offsetcorrection value setting processing 860, offset compensation valueupdating processing 670, and offset correction processing 680 as initialsetting. Examples of the parameters to be set include the offsetcorrection unit Ofst_u to be used for the offset correction valuesetting processing, the address minimum value adrsMin and maximum valueadrsMax within each LUT where a distortion compensation coefficient tobe corrected in the offset correction processing is stored, offsetcompensation values Ofst_m1 and Ofst_m2 to be stored in the compensationvalue storage units 436 and 440 in the offset compensation valueupdating processing, and an offset amount determining threshold Ofst_thfor determining the range of the offset amount serving as adetermination reference in the offset amount determination processing.

Though not particularly restricted, a certain positive value u_(o) isset as the offset correction unit Ofst_u, and 0 (zero) is set as theoffset compensation values Ofst_m1 and Ofst_m2.Ofst_(—) u=u _(o)Ofst_(—) m1=0, Ofst_(—) m2=0

Also, though not particularly restricted, the minimum value A_(min) andmaximum value A_(max) of addresses where a correction coefficient isstored in the respective LUT are set as the address minimum valueadrsMin and maximum value adrsMax to be corrected, respectively.adrsMin=A _(min)adrsMax=A _(max)

Also, though not particularly restricted, a certain positive value th₀is set as the offset amount determining threshold Ofst_th.Ofst_(—) th=th _(o)

Next, according to the steps S606 through S610, an LUT to be processedis selected, and the calculation processing 650 of the offset amountLUTofst_x as to the selected LUTx to be processed is performed (x is anyof a through d). The details of the processing performed in steps S606through S610 is as described in the flowchart in FIG. 6.

Next, in step S811, the offset control unit 732 determines whether ornot the calculated offset amount LUTOfst_x is a value within a rangedetermined by the offset determining threshold Ofst_th set in step S804,i.e., whether or not the following Expression 2 is satisfied−Ofst_(—) th≦LUTOfst_(—) x≦+Ofst_(—) th  Expression 2(−th ₀≦LUTOfst_(—) x+th ₀)

In the event that the offset control unit 732 has determined in stepS811 that the calculated offset amount LUTofst_x is a value within therange indicated by the above Expression 2, the processing proceeds tostep S813.

In step S813, the offset control unit 732 sets 0 (zero) as the offsetcorrection value Ofst_x as to the LUTx to be processed. After settingthe offset correction value, the processing proceeds to step S630.Ofst_(—) x=0

Specifically, when determining that the offset amount LUTofst_x is avalue within the range indicated by the above Expression 2, the offsetcontrol unit 732 performs the distortion compensation coefficientupdating processing in step S630 without executing the offsetcompensation value updating processing 670 nor offset correctionprocessing 680.

On the other hand, in the event that the offset control unit 732 hasdetermined in step S811 that the calculated offset amount LUTofst_x is avalue out of the range indicated by the above Expression 2 (is not avalue within the range indicated by the above Expression 2), theprocessing proceeds to step S812.

In step S812, when determining that the offset amount LUTofst_x is avalue greater than the upper limit +Ofst_th (=+th₀), the offset controlunit 732 performs processing for setting a value other than 0 (zero) asthe offset correction value Ofst_x as to the LUTx to be processed usingthe offset correction unit Ofst_u as follows. That is to say, the offsetcontrol unit 432 sets a certain positive value u₀ as the offsetcorrection value.Ofst_(—) x=+Ofst_(—) u=+u ₀

When determining in step S812 that the offset amount LUTofst_x is avalue smaller than the lower limit −Ofst_th (=−th₀), the offset controlunit 732 performs processing for setting a value other than 0 (zero) asthe offset correction value Ofst_x as to the LUTx to be processed usingthe offset correction unit Ofst_u as follows. That is to say, the offsetcontrol unit 432 sets a certain negative value −u_(o) as the offsetcorrection value.Ofst_(—) x=−Ofst_(—) u=−u ₀

After setting the offset correction value in step S812, the processingproceeds to step S614.

According to the above steps S811 through S813, the offset amountdetermination processing 855 and offset correction value settingprocessing 860 are performed at the offset correction processing unit770.

Next, according to steps S614 through S628, the offset compensationvalue updating processing 670 and offset correction processing 680 areperformed as to the LUTx to be processed (x is any of a through d). Thedetails of the processing performed in steps S614 through S628 are asdescribed above in the flowchart in FIG. 6.

A series of processing performed by the above steps S604 through S628and S811 through S813 is the distortion compensation coefficientcorrection processing that the distortion compensation apparatus 702executes.

Also, in step S630, the distortion compensation coefficient updatingunit 324 performs the distortion compensation coefficient updatingprocessing as to each LUT. The distortion compensation coefficientupdating processing is as described in the flowchart in FIG. 6. Afterthe distortion compensation coefficient updating processing, theprocessing returns to step S606.

As described above, with the distortion compensation coefficientcorrection and updating processing illustrated in FIG. 8, in the sameway as with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 6, according to the offsetamount calculation processing 650 and offset correction processing 680,a distortion compensation coefficient is clipped to the upper limit orlower limit of the coefficient setting range, whereby the distortioncompensation performance can be suppressed from deterioration. Further,according to the offset compensation value updating processing 670, evenin the event that the value of the distortion compensation coefficientstored in each LUT is corrected by the offset correction processing 680,suitable distortion compensation processing can be performed using adistortion compensation coefficient generated in a pseudo manner.

Further, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 8, in the same way as with thedistortion compensation coefficient correction and updating processingillustrated in FIG. 6, according to the offset correction value settingprocessing 860, a suitable value according to the calculated offsetamount can be set as the offset correction value of a distortioncompensation coefficient, and also the value of the offset correctionunit Ofst_u is suitably adjusted, whereby the influence of the offsetcorrection processing 680 to be applied to the convergence of adistortion compensation coefficient in the distortion compensationcoefficient updating processing can be suppressed small.

In addition, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 8, according to the offsetamount determination processing 855, determination is made whether ornot the calculated offset amount is a value within a predeterminedrange, whereby whether to execute the offset correction processing 680and offset compensation value updating processing 670 can selectively becontrolled according to the determination result thereof.

Thus, the offset control unit 732 can be controlled so that when themagnitude (absolute value) of the calculated offset amount is smallerthan a certain threshold, and necessity to perform the offset correctionprocessing of the distortion compensation coefficient at each LUT islow, the offset correction processing 680 and offset compensation valueupdating processing 670 are not executed, and when the magnitude(absolute value) of the calculated offset amount is greater than acertain threshold, and necessity to perform the offset correctionprocessing of the distortion compensation coefficient at each LUT ishigh, the offset correction processing 680 and offset compensation valueupdating processing 670 are selectively executed, and accordingly, eachprocess can more effectively be executed not only at the offset controlunit 732 but also at the compensation value storage units 436 and 400and each of the LUTa 406 through LUTd 412.

Accordingly, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 8, the power consumption of theoffset correction processing unit 770 and distortion compensationcoefficient supplying unit 450 can be reduced, and the power consumptionof the distortion compensation apparatus 702 can be reduced.

3. Third Embodiment

Hereafter, description will be made regarding a wireless communicationdevice and a distortion compensation apparatus, according to a thirdembodiment.

3-1. Configuration Example of Pre-Distortion Signal Generating Unit 922

Though the configuration of a wireless communication device 900according to the third embodiment differs from the configuration of thewireless communication device 300 illustrated in FIG. 3 in that adistortion compensation apparatus 902 and a pre-distortion signalgenerating unit 922 are provided instead of the distortion compensationapparatus 302 and pre-distortion signal generating unit 322, portionsother than those are the same. Accordingly, with regard to theconfiguration of the wireless communication apparatus 900, drawingthereof is omitted.

FIG. 9 is a diagram illustrating an example of the internalconfiguration of the pre-distortion signal generating unit 922. Thoughthe internal configuration of the pre-distortion signal generating unit922 differs from the internal configuration of the pre-distortion signalgenerating unit 322 illustrated in FIG. 4 in that an offset control unit932 and an offset correction processing unit 970 are provided instead ofthe offset control unit 432 and offset correction processing unit 470,portions other than those are the same. In FIG. 9, the same orcorresponding portions are denoted with the same reference numerals aswith the pre-distortion signal generating unit 322 illustrated in FIG.4.

As illustrated in FIG. 9, the pre-distortion signal generating unit 922includes a distortion compensation coefficient supplying unit 450, adistortion compensation processing unit 460, and an offset correctionprocessing unit 970. The offset correction processing unit 970 includesan offset control unit 932, compensation value storage units 436 and440, and offset compensation units 438 and 442. The offset control unit932 includes a mean value calculating unit 434 in the same way as withthe offset control unit 432, and also includes a maximum power searchunit 950 configured to search the maximum power of the transmissionsignal Tx(t).

With the offset correction processing unit 970, the offset control unit932 executes processing for search the maximum power of the transmissionsignal Tx(t) after a series of processing, such as the offset amountcalculation processing and offset correction processing, are executed.

The maximum power search unit 950 of the offset control unit 932receives the transmission signal Tx(t), and calculates the power valuep(t) of the transmission signal Tx(t) based on the amplitude of thereceived transmission signal Tx(t). The maximum power search unit 950monitors the power value p(t) of the transmission signal Tx(t) for acertain period of time, and determines a maximum power value p_spec outof the power value p(t) obtained for the certain period of time thereof.

The maximum power search unit 950 determines whether or not thedetermined maximum power value p_spec is greater than the currentmaximum power value p_max corresponding to the current address maximumvalue adrsMax to be corrected.

When determining that the determined maximum power value p_spec isgreater than the current maximum power value p_max corresponding to thecurrent address maximum value adrsMax to be corrected (p_spec>p_max),the maximum power search unit 950 updates the value of the addressmaximum value adrsMax to be corrected to the address value correspondingto the determined maximum power value p_spec.

On the other hand, when determining that the determined maximum powervalue p_spec is equal to or smaller than the current maximum power valuep_max corresponding to the current address maximum value adrsMax to becorrected (p_spec≦p_max, not greater than the current maximum powervalue p_max), the maximum power search unit 950 does not update theaddress maximum value adrsMax to be corrected, and maintains the currentvalue.

The offset control unit 932 executes a series of the processing such asthe offset amount calculation processing and offset correctionprocessing and so forth again using the address maximum value adrsMax tobe corrected after the maximum power search processing by the maximumpower search unit 950.

Here, of all of the compensation coefficient h(p(t)) within each LUT,the distortion compensation coefficient stored in the addresscorresponding to the power value greater than the maximum power valuep_max of the transmission signal Tx(t) is a coefficient that has notever been used since the transmission signal Tx(t) having thecorresponding power value has not been input during the operation of thedistortion compensation apparatus 902, and is a coefficient with noupdating processing being performed. Therefore, it can be conceived thatthe offset correction processing does not have to be performed regardingthe distortion compensation coefficient stored in the addresscorresponding to a power value greater than the maximum power valuep_max.

On the other hand, with the distortion compensation apparatus 902, theaddress maximum value adrsMax to be corrected has been determined usingthe maximum power value p_max of the transmission signal Tx(t) that hasbeen input up to now, and accordingly, the address region to becorrected of each LUT to be accessed in the offset amount calculationprocessing or offset correction processing can be set based on themaximum power value p_max of the transmission signal Tx(t). Thus, anaddress where a distortion compensation coefficient that does not haveto be subjected to the offset correction processing is stored can beexcluded from addresses to be accessed, and accordingly, the operationof the offset amount calculation processing or offset correctionprocessing at the offset control unit 932 can more effectively beperformed.

Accordingly, with the distortion compensation apparatus 902, the powerconsumption of the offset correction processing unit 970 and distortioncompensation coefficient supplying unit 450 can be reduced.

Note that, with the above embodiment, the power value of thetransmission signal Tx(t) has been monitored for a certain period oftime, thereby determining the maximum power value p_spec during thecertain period of time thereof, and the address region to be correctedof each LUT to be accessed has been set based on the determined maximumpower value p_spec, but further, an arrangement may be made wherein theminimum power value for the certain period of time thereof isdetermined, and the address region to be corrected of each LUT to beaccessed is set based on the determined minimum power value. In thiscase, according to the offset control unit 932, determination is madewhether or not the determined minimum power value is smaller than thecurrent minimum power value p_min corresponding to the current addressminimum value adrsMin to be corrected, and in the event thatdetermination is made that the determined minimum power value is smallerthan the current minimum power value p_min, the address minimum valueadrsMin to be corrected may be updated to the value of an addresscorresponding to the determined minimum power value.

3-2. Example of Distortion Compensation Coefficient Correction andUpdating Operation at Distortion Compensation Apparatus 902

FIG. 10 is a diagram illustrating an example of a flowchart ofdistortion compensation coefficient correction and updating processingat the distortion compensation apparatus 902 according to the thirdembodiment. With the flowchart of the distortion compensationcoefficient correction and updating processing illustrated in FIG. 10,the same or corresponding steps are denoted with the same referencenumerals as with the steps of the flowchart illustrated in FIG. 6.Hereafter, description will be made regarding the distortioncompensation coefficient correction and updating processing that thedistortion compensation apparatus 902 executes, with reference to theflowchart in FIG. 10. Note that, with the flowchart in FIG. 10, anumeric expression relating to the processing in the corresponding stepis indicated in a portion surrounded with a dotted line.

First, in step S602, the distortion compensation apparatus 902 starts aseries of the distortion compensation coefficient correction andupdating processing.

Next, in step S604, the offset control unit 932 of the offset correctionprocessing unit 970 sets parameters used for the offset correction valuesetting processing 660, offset compensation value updating processing670, and offset correction processing 680 as initial setting. Examplesof the parameters to be set include the offset correction unit Ofst_u tobe used for the offset correction value setting processing, the addressminimum value adrsMin and maximum value adrsMax within each LUT where adistortion compensation coefficient to be corrected in the offsetcorrection processing is stored, and offset compensation values Ofst_m1and Ofst_m2 to be stored in the compensation value storage units 436 and440 in the offset compensation value updating processing.

Though not particularly restricted, a certain positive value u_(o) isset as the offset correction unit Ofst_u, and 0 (zero) is set as theoffset compensation values Ofst_m1 and Ofst_m2.Ofst_(—) u=u _(o)Ofst_(—) m1=0, Ofst_(—) m2=0

Also, though not particularly restricted, the minimum value A_(min) ofan address where a compensation coefficient is stored at each LUT is setas the address minimum value adrsMin to be corrected.adrsMin=A _(min)

Also, though not particularly restricted, a predicted value A_(exp) tobe predicted as the maximum value of the power value of the transmissionsignal Tx(t) that the distortion compensation apparatus 902 receives isset as the address maximum value adrsMax to be corrected.adrsMax=A _(exp)

Next, according to the steps S606 through S628, an LUT to be processedis selected, and the offset control unit 932 executes the offset amountcalculation processing 650, offset correction value setting processing660, offset compensation value updating processing 670, and offsetcorrection processing 680 as to the selected LUTx to be processed (x isany of a through d).

Next, in step S630, the distortion compensation coefficient updatingunit 324 executes the distortion compensation updating processing as toeach LUT. The details of the processing performed in steps S606 throughS630 is as described in the flowchart in FIG. 6.

Next, in step S1032, the maximum power search unit 950 of the offsetcontrol unit 932 receives the transmission signal Tx(t), and calculatesthe power value p(t) of the transmission signal Tx(t) based on theamplitude of the received transmission signal Tx(t). The maximum powersearch unit 950 continuously monitors the power value p(t) of thetransmission signal Tx(t) for a certain period of time, and determines amaximum power value p_spec by searching the maximum value out of thepower value p(t) obtained for the certain period of time thereof.

Next, in step S1034, the maximum power search unit 950 obtains thecorresponding current maximum power value p_max based on the currentlyset address maximum value adrsMax to be corrected. The maximum powersearch unit 950 determines whether or not the maximum power value p_specdetermined in step S1032 is greater than the corresponding currentmaximum power value p_max.

When determining that the determined maximum power value p_spec isgreater than the current maximum power value p_max (p_spec>p_max), theprocessing proceeds to step S1036.

On the other hand, when determining that the determined maximum powervalue p_spec is equal to or smaller than the current maximum power valuep_max (p_spec≦p_max, not greater than the current maximum power valuep_max), the processing returns to step S606. At this time, the maximumpower search unit 950 does not update the value of the address maximumvalue adrsMax to be corrected, and maintains the currently set value asthe value of the address maximum value adrsMax to be corrected.

Next, in step S1036, the maximum power search unit 950 generates thecorresponding address value adrsUpd based on the maximum power valuep_spec determined in step S1032. The maximum power search unit 950updates the address maximum value adrsMax to be corrected, to thegenerated address value adrsUpd.adrsMax=adrsUpd

After the updating processing of the address maximum value adrsMax, theprocessing returns to step S606.

According to the above steps S1032 through S1036, the maximum powersearch processing 1090 is performed at the offset correction processingunit 970.

A series of processing performed by the above steps S604 through S628and S1032 through S1036 is the distortion compensation coefficientcorrection processing that the distortion compensation apparatus 902executes.

In step S606 and thereafter, the offset control unit 932 executes theseries of the distortion compensation coefficient correction andupdating processing again using the updated address maximum valueadrsMax to be corrected.

As described above, with the distortion compensation coefficientcorrection and updating processing illustrated in FIG. 10, in the sameway as with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 6, a distortion compensationcoefficient is clipped to the upper limit or lower limit in thecoefficient setting range by the offset amount calculation processing650 and offset correction processing 680, whereby the distortioncompensation performance can be suppressed from deterioration. Further,according to the offset compensation value updating processing 670, evenin the event that the value of the distortion compensation coefficientstored in each LUT has been corrected by the offset correctionprocessing 680, suitable distortion compensation processing can beperformed using a distortion compensation coefficient generated in apseudo manner.

Further, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 10, in the same way as with thedistortion compensation coefficient correction and updating processingillustrated in FIG. 6, according to the offset correction value settingprocessing 760, a suitable value according to the calculated offsetamount can be set as the offset correction value of a distortioncompensation coefficient, and also the value of the offset correctionunit Ofst_u is suitably adjusted, whereby the offset correctionprocessing 680 can suppress influence to be applied to the convergenceof a distortion compensation coefficient small in the distortioncompensation coefficient updating processing.

In addition, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 10, according to the maximumpower search processing 1090, the address maximum value adrsMax to becorrected is determined with the maximum power value p_max of thetransmission signal Tx(t) that has been input up to now, whereby anaddress region to be corrected at each LUT to be accessed in the offsetamount calculation processing and offset correction processing can beset based on the maximum power value p_max of the transmission signalTx(t).

Accordingly, an address corresponding to a power value greater than themaximum power value p_max of the transmission signal Tx(t), where adistortion compensate coefficient of which the necessity to perform theoffset correction processing is low is stored, can be excluded fromaddresses to be accessed by the maximum power search processing 1090,and accordingly, each process can more effectively be executed not onlyat the offset control unit 932 but also at each of the LUTa 406 throughLUTd 412.

Accordingly, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 10, the power consumption of theoffset correction processing unit 970 and distortion compensationcoefficient supplying unit 450 can be reduced, and the power consumptionof the distortion compensation apparatus 902 can be reduced.

Note that, with the flowchart in FIG. 10, with regard to processingother than the maximum power search processing 1090, though an exampleemploying the distortion compensation coefficient correction andupdating processing according to the first embodiment is illustrated inFIG. 6 has been described, the present disclosure is not restricted tothis, and the distortion compensation coefficient correction andupdating processing according to the second embodiment illustrated inFIG. 8 may be employed, for example.

4. Fourth Embodiment

Hereafter, description will be made regarding a wireless communicationdevice and a distortion compensation apparatus, according to a fourthembodiment.

4-1. Configuration Example of Pre-Distortion Signal Generating Unit 1122

Though the configuration of a wireless communication device 1110according to the fourth embodiment differs from the configuration of thewireless communication device 300 illustrated in FIG. 3 in that adistortion compensation apparatus 1102 and a pre-distortion signalgenerating unit 1122 are provided instead of the distortion compensationapparatus 302 and pre-distortion signal generating unit 322, portionsother than those are the same. Accordingly, with regard to theconfiguration of the wireless communication apparatus 1100, drawingthereof is omitted.

FIG. 11 is a diagram illustrating an example of the internalconfiguration of the pre-distortion signal generating unit 1122. FIG. 12is a diagram for describing the distortion compensation coefficientcorrection processing at the pre-distortion signal generating unit 1122.Hereafter, a configuration example of the pre-distortion signalgenerating unit 1122 will be described with reference to FIGS. 11 and12.

Though the internal configuration of the pre-distortion signalgenerating unit 1122 differs from the internal configuration of thepre-distortion signal generating unit 322 illustrated in FIG. 4 in thatan offset control unit 1132 and an offset correction processing unit1170 are provided instead of the offset control unit 432 and offsetcorrection processing unit 470, compensation value storage units 1135through 1137 and 1139 through 1141 are provided instead of thecompensation value storage units 436 and 440, and offset compensationunits 1138 and 1142 are provide instead of the offset compensation units438 and 442, portions other than those are the same. In FIG. 11, thesame or corresponding portions are denoted with the same referencenumerals as with the pre-distortion signal generating unit 322illustrated in FIG. 4.

As illustrated in FIG. 11, the pre-distortion signal generating unit1122 includes a distortion compensation coefficient supplying unit 450,a distortion compensation processing unit 460, and an offset correctionprocessing unit 1170. The offset correction processing unit 1170includes an offset control unit 1132, compensation value storage units1135 through 1137 and 1139 through 1141, and offset compensation units1138 and 1142. The offset control unit 1132 includes a mean valuecalculating unit 434 in the same way as with the offset control unit432.

In general, the frequency of occurrence of the transmission signal Tx(t)that the distortion compensation apparatus receives has bias regardingthe power value p(t) thereof. Specifically, the transmission signalTx(t) has a tendency wherein, with a range of the power valuecorresponding to an address region to be corrected, the frequency ofoccurrence of a transmission signal having a medium-sized power value ishigh, and the frequency of occurrence of a transmission signal having asmall power value and a transmission signal having a great power valueis low. With regard to the distortion compensation coefficient h(p(t))corresponding to a power value p(t) of which the frequency of occurrenceis low, a frequency where coefficient updating processing is performedis also low.

Therefore, with regard to a distortion compensation coefficientcorresponding to a power value smaller or greater than the abovemedium-sized power value, the actual offset amount thereof is apt to begenerally smaller than the offset amount LUTofst in the case of beingcalculated as the mean value of the distortion compensation coefficientsof the entire address region to be corrected. Conversely, the actualoffset amount of the distortion compensation coefficient h(p(t))corresponding to the above medium-sized power value p(t) is apt to begenerally greater than the offset amount LUTofst in the case of beingcalculated as the mean value of the distortion compensation coefficientsof the entire address region to be corrected. In this way, in general,unbalance regarding the offset amount within the address region to becorrected is caused.

On the other hand, the offset correction processing unit 1170 setsmultiple divided address regions within the address region to becorrected within each LUT based on the power value p(t) of thetransmission signal Tx(t), and executes each process relating to thedistortion compensation coefficient correction processing independentlyfor every set multiple address regions.

Specifically, as illustrated in FIG. 12 for example, the offset controlunit 1132 sets three divided regions of an address region 1202 having amedium-sized address corresponding to a power value of which thefrequency of occurrence is higher, an address region 1201 having asmaller address than the address region 1202 corresponding to a powervalue of which the frequency of occurrence is lower, and an addressregion 1203 having a greater address than the address region 1202corresponding to a power value of which the frequency of occurrence islower, within in the address region to be corrected of each LUT.

The offset control unit 1132 executes a series of processing includingthe offset amount calculation processing, offset correction valuesetting processing, offset compensation value updating processing, andoffset correction processing, independently for every three addressregions 1201 through 1203 at each LUT.

The offset control unit 1132 calculates, with the offset amountcalculation processing, three offset amounts LUTosft_x1 throughLUTosft_x3 corresponding to the address regions 1201 through 1203, foreach of the LUTs. The offset control unit 1132 performs settingprocessing of the offset correction values Ofst_x1 through Ofst_x3independently for every address regions 1201 through 1203 based on thecalculated offset amounts LUTosft_x1 through LUTosft_x3, for each of theLUTs. The offset control unit 1132 performs the offset correctionprocessing as to the distortion compensation coefficient stored in eachaddress region independently for every address regions 1201 through 1203based on the set offset correction values Ofst_x1 through Ofst_x3, foreach of the LUTs.

Also, the offset control unit 1132 sets three offset compensation valuesOfst_m11, Ofst_m12, and Ofst_m13 corresponding to the address regions1201, 1202, and 1203 as the offset compensation values to be supplied tothe offset compensation unit 1138 in response to the three offsetamounts LUTosft_x1 through LUTosft_x3 being calculated. The offsetcompensation values Ofst_m11 through Ofst_m13 are stored in the threecompensation value storage units 1135 through 1137, respectively.

The offset control unit 1132 calculates, with the offset compensationvalue updating processing, the updated values of the offset compensationvalues Ofst_m11 through Ofst_m13 independently for every three addressregions 1201 through 1203, and stores the calculated updated values ofthe offset compensation values Ofst_m11 through Ofst_m13 in thecompensation value storage units 1135 through 1137.

Similarly, the offset control unit 1132 sets three offset compensationvalues Ofst_m21, Ofst_m22, and Ofst_m23 corresponding to the addressregions 1201, 1202, and 1203 as the offset compensation values to besupplied to the offset compensation unit 1142. The offset compensationvalues Ofst_m21 through Ofst_m23 are stored in the three compensationvalue storage units 1139 through 1141, respectively.

The offset control unit 1132 calculates, with the offset compensationvalue updating processing, the updated values of the offset compensationvalues Ofst_m21 through Ofst_m23 independently for every three addressregions 1201 through 1203, and stores the calculated updated values ofthe offset compensation values Ofst_m21 through Ofst_m23 in thecompensation value storage units 1139 through 1141.

The offset compensation unit 1138 receives the offset compensationvalues Ofst_m11 through Ofst_m13 from the compensation value storageunits 1135 through 1137. Also, the offset compensation unit 1138receives the address Adrs(Tx(t)) from the address generating unit 402,and determines which of the address regions 1201 through 1203 the valueof the received address Adrs(Tx(t)) corresponds to. The offsetcompensation unit 1138 selects one value out of the received offsetcompensation values Ofst_m11 through Ofst_m13 according to thedetermination result thereof. The offset compensation unit 1138 performsthe offset compensation processing as to the post-synthesis coefficienth1(p(t)) output from the adder 414 using the selected offsetcompensation value.

Similarly, the offset compensation unit 1142 receives the offsetcompensation values Ofst_m21 through Ofst_m23 from the compensationvalue storage units 1139 through 1141. Also, the offset compensationunit 1142 receives the address Adrs(Tx(t−1) corresponding to theprevious reference point-in-time t−1 from the delay unit 404, anddetermines which of the address regions 1201 through 1203 the receivedaddress Adrs(Tx(t−1)) corresponds to. The offset compensation unit 1142selects one value out of the received offset compensation valuesOfst_m21 through Ofst_m23 according to the determination result thereof.The offset compensation unit 1142 performs the offset compensationprocessing as to the post-synthesis coefficient h2(p(t)) output from theadder 416 using the selected offset compensation value.

Thus, with the distortion compensation apparatus 1102, multiple addressregions are set within the address region to be corrected as to eachLUT, and multiple offset amounts corresponding to the set multipleaddress regions are calculated, and accordingly, even in the event thatthe frequency of occurrence of the transmission signal Tx(t) has biasregarding the power value p(t), a more accurate offset amountcorresponding to the power value (address value) thereof can becalculated as to the distortion compensation coefficient within eachLUT. Thus, unbalance regarding the offset amount caused within theaddress to be corrected within each LUT can be reduced, whereby theoffset correction processing of the distortion compensation coefficientwithin each LUT can more precisely be controlled.

Accordingly, with the distortion compensation apparatus 1102, theprecision of the offset correction processing of the distortioncompensation coefficient within each LUT can be improved.

Note that, with the above embodiment, though an arrangement has beenmade wherein the three compensation value storage units 1135 through1137 are provided in response to the three address regions 1201 through1203, the present disclosure is not restricted to this, and anarrangement may be made for example wherein three storage regionscorresponding to the address regions 1201 through 1203 are providedwithin one offset compensation storage unit, and the offset compensationvalues Ofst_m11 through Ofst_m13 are stored in these three storageregions. This can also be applied to the compensation value storageunits 1139 through 1141.

Also, the number of address regions to be set to the address region tobe corrected is not restricted to three, and the number of addressregions can be changed as appropriate.

4-2. Example of Distortion Compensation Coefficient Correction andUpdating Operation at Distortion Compensation Apparatus 1102

FIG. 13 is a diagram illustrating an example of a flowchart ofdistortion compensation coefficient correction and updating processingat the distortion compensation apparatus 1102 according to the fourthembodiment. Hereafter, description will be made regarding the distortioncompensation coefficient correction and updating processing that thedistortion compensation apparatus 1102 executes, with reference to theflowchart in FIG. 13. Note that, with the flowchart in FIG. 13, anumeric expression relating to the processing in the corresponding stepis indicated in a portion surrounded with a dotted line.

First, in step S1302, the distortion compensation apparatus 1102 startsa series of the distortion compensation coefficient correction andupdating processing.

Next, in step S1304, the offset control unit 1132 of the offsetcorrection processing unit 1170 sets parameters used for offsetcorrection value setting processing, offset compensation value updatingprocessing, and offset correction processing in later-described stepsS1308 through S1330 as initial setting.

Examples of the parameters to be set include the offset correction unitOfst_u to be used for the offset correction value setting processing,the address minimum value adrsMin and maximum value adrsMax within eachLUT where a distortion compensation coefficient to be corrected in theoffset correction processing is stored, a boundary address value ardsTh1specifying the value of an address serving as the boundary between theaddress region 1201 and the address region 1202, a boundary addressvalue ardsTh2 specifying the value of an address serving as the boundarybetween the address region 1202 and the address region 1203, and theoffset compensation values Ofst_m11 through Ofst_m13 and Ofst_m21through Ofst_m23 to be stored in the compensation value storage units1135 through 1137 and 1139 through 1141 in the offset compensation valueupdating processing.

Though not particularly restricted, a certain positive value u_(o) isset as the offset correction unit Ofst_u.Ofst_(—) u=u _(o)

Also, 0 (zero) is set as each of the offset compensation values Ofst_m11through Ofst_m13 and Ofst_m21 through Ofst_m23.Ofst_(—) m11=0, Ofst_(—) m12=0Ofst_(—) m13=0Ofst_(—) m21=0, Ofst_(—) m22=0Ofst_(—) m23=0

Also, though not particularly restricted, the minimum value A_(min) andmaximum value A_(max) of addresses where a correction coefficient isstored in the respective LUT are set as the address minimum valueadrsMin and maximum value adrsMax to be corrected, respectively.adrsMin=A _(min)adrsMax=A _(max)

Also, though not particularly restricted, predetermined certain addressvalues A_(th1) and A_(th2) are set as the boundary address valuesadrsTh1 and adrsTh2, respectively.adrsTh1=A _(th1)adrsTh2=A _(th2)

Next, in step S1306, the offset control unit 1132 selects one LUT to beprocessed out of the LUTa 406 through LUTd 412. The offset control unit1132 cyclically selects the corresponding LUT in the sequence of LUTa406, LUTb 408, LUTc 410, LUTd 412, LUTa 406, LUTb 408, and so on, forexample.

Next, in step S1308, the offset control unit 1132 performs processingfor calculating the offset amount LUTofst_x1 of a distortioncompensation coefficient as to the address region 1201 of the LUT_x tobe processed (x is any of a through d) selected in step S1306. Thisoffset amount calculation processing is the same as the offset amountcalculation processing 650 described in the flowchart in FIG. 6 exceptthat the distortion compensation coefficient h(p(t)) to be subjected tothe addition averaging operation indicated by the above Expression 1 arecoefficients stored in the address region from the address minimum valueadrsMin to the boundary address value adrsTh1.

Next, in step S1310, the offset control unit 1132 performs processingfor setting the offset correction value Ofst_x1 as to the address region1201 of the LUT_x to be processed. This offset correction value settingprocessing is the same as the offset correction value setting processing660 described with the flowchart in FIG. 6.

Next, in step S1312, the offset control unit 1132 performs processingfor updating the offset compensation values Ofst_m11 and Ofst_m21corresponding to the address regions 1201 in the respective LUT. Thisoffset compensation value updating processing is the same as the offsetcompensation value updating processing 670 described with the flowchartin FIG. 6.

Now, in the event that the LUT to be processed selected in step S1306 isthe LUTa or LUTb, the offset control unit 1132 stores the updated valueOfst_m of the offset compensation value in the compensation valuestorage unit 1135, and updates the offset compensation value Ofst_m11within the compensation value storage unit 1135.

Also, in the event that the LUT to be processed selected in step S1306is the LUTc or LUTd, the offset control unit 1132 stores the updatedvalue Ofst_m of the offset compensation value in the compensation valuestorage unit 1139, and updates the offset compensation value Ofst_m21within the compensation value storage unit 1139.

Next, in step S1314, the offset control unit 1132 performs the offsetcorrection processing as to the distortion compensation coefficienth(p(t)) stored in the address region 1201 of the LUTx to be processed.This offset correction processing is the same as the offset correctionprocessing 680 described with the flowchart in FIG. 6 except that thedistortion compensation coefficient h(p(t)) to be subjected to thecorrection processing are coefficients stored in the address region fromthe address minimum value adrsMin to the boundary address value adrsTh1.

According to the above steps S1308 through S1314, the distortioncompensation coefficient correction processing 1350 as to the addressregion 1201 is performed at the offset correction processing unit 1170.

Next, in step S1316, the offset control unit 1132 performs processingfor calculating the offset amount LUTofst_x2 of a distortioncompensation coefficient as to the address region 1202 of the LUT_x tobe processed (x is any of a through d) selected in step S1306. Thisoffset amount calculation processing is the same as the offset amountcalculation processing 650 described in the flowchart in FIG. 6 exceptthat the distortion compensation coefficient h(p(t)) to be subjected tothe addition averaging operation indicated by the above Expression 1 arecoefficients stored in the address region from the boundary addressvalue adrsTh1 to the boundary address value adrsTh2.

Next, in step S1318, the offset control unit 1132 performs processingfor setting the offset correction value Ofst_x2 as to the address region1202 of the LUT_x to be processed. This offset correction value settingprocessing is the same as the offset correction value setting processing660 described with the flowchart in FIG. 6.

Next, in step S1320, the offset control unit 1132 performs processingfor updating the offset compensation values Ofst_m13 and Ofst_m22corresponding to the address regions 1202 in the respective LUT. Thisoffset compensation value updating processing is the same as the offsetcompensation value updating processing 670 described with the flowchartin FIG. 6.

Now, in the event that the LUT to be processed selected in step S1306 isthe LUTa or LUTb, the offset control unit 1132 stores the updated valueOfst_m of the offset compensation value in the compensation valuestorage unit 1136, and updates the offset compensation value Ofst_m12within the compensation value storage unit 1136.

Also, in the event that the LUT to be processed selected in step S1306is the LUTc or LUTd, the offset control unit 1132 stores the updatedvalue Ofst_m of the offset compensation value in the compensation valuestorage unit 1140, and updates the offset compensation value Ofst_m22within the compensation value storage unit 1140.

Next, in step S1322, the offset control unit 1132 performs the offsetcorrection processing as to the distortion compensation coefficienth(p(t)) stored in the address region 1202 of the LUT_x to be processed.This offset correction processing is the same as the offset correctionprocessing 680 described with the flowchart in FIG. 6 except that thedistortion compensation coefficient h(p(t)) to be subjected to thecorrection processing are coefficients stored in the address region fromthe boundary address value adrsTh1 to the boundary address valueadrsTh2.

According to the above steps S1316 through S1322, the distortioncompensation coefficient correction processing 1360 as to the addressregion 1202 is performed at the offset correction processing unit 1170.

Next, in step S1324, the offset control unit 1132 performs processingfor calculating the offset amount LUTofst_x3 of a distortioncompensation coefficient as to the address region 1203 of the LUT_x tobe processed (x is any of a through d) selected in step S1306. Thisoffset amount calculation processing is the same as the offset amountcalculation processing 650 described in the flowchart in FIG. 6 exceptthat the distortion compensation coefficient h(p(t)) to be subjected tothe addition averaging operation indicated by the above Expression 1 arecoefficients stored in the address region from the boundary addressadrsTh2 to the address maximum value adrsMax.

Next, in step S1326, the offset control unit 1132 performs processingfor setting the offset correction value Ofst_x3 as to the address region1203 of the LUT_x to be processed. This offset correction value settingprocessing is the same as the offset correction value setting processing660 described with the flowchart in FIG. 6.

Next, in step S1328, the offset control unit 1132 performs processingfor updating the offset compensation values Ofst_m13 and Ofst_m23corresponding to the address regions 1203 in the respective LUT. Thisoffset compensation value updating processing is the same as the offsetcompensation value updating processing 670 described with the flowchartin FIG. 6.

Now, in the event that the LUT to be processed selected in step S1306 isthe LUTa or LUTb, the offset control unit 1132 stores the updated valueOfst_m of the offset compensation value in the compensation valuestorage unit 1137, and updates the offset compensation value Ofst_m13within the compensation value storage unit 1137.

Also, in the event that the LUT to be processed selected in step S1306is the LUTc or LUTd, the offset control unit 1132 stores the updatedvalue Ofst_m of the offset compensation value in the compensation valuestorage unit 1141, and updates the offset compensation value Ofst_m23within the compensation value storage unit 1141.

Next, in step S1330, the offset control unit 1132 performs the offsetcorrection processing as to the distortion compensation coefficienth(p(t)) stored in the address region 1203 of the LUT_x to be processed.This offset correction processing is the same as the offset correctionprocessing 680 described with the flowchart in FIG. 6 except that thedistortion compensation coefficient h(p(t)) to be subjected to thecorrection processing are coefficients stored in the address region fromthe boundary address value adrsTh2 to the address maximum value adrsMax.

According to the above steps S1324 through S1330, the distortioncompensation coefficient correction processing 1370 as to the addressregion 1203 is performed at the offset correction processing unit 1170.

A series of processing performed by the above steps S1304 through S1330is the distortion compensation coefficient correction processing thatthe distortion compensation apparatus 1102 executes.

Next, in step S1332, the compensation coefficient updating unit 324performs distortion compensation coefficient updating processing as tothe respective LUT. The details of this distortion compensationcoefficient updating processing are as described with the flowchart inFIG. 6. After the distortion compensation coefficient updatingprocessing, the processing returns to step S1306.

In step S1306, the offset control unit 1132 selects another LUT out ofthe LUTa 406 through LUTd 412 as the next LUT to be corrected. Theoffset control unit 1132 executes the distortion compensationcoefficient correction processing 1350 through 1370 as to the addressregions 1201 through 1203 regarding the selected LUT to be corrected.

As described above, with the distortion compensation coefficientcorrection and updating processing illustrated in FIG. 13, in the sameway as with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 6, according to the offsetamount calculation processing and offset correction processing, adistortion compensation coefficient is clipped to the upper limit orlower limit in the coefficient setting range, whereby the distortioncompensation performance can be suppressed from deterioration. Further,according to the offset compensation value updating processing 670, evenin the event that the value of the distortion compensation coefficientwithin each LUT has been corrected by the offset correction processing680, suitable distortion compensation processing can be performed usingthe distortion compensation coefficient generated in a pseudo manner.

Further, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 13, in the same way as with thedistortion compensation coefficient correction and updating processingillustrated in FIG. 6, according to the offset correction value settingprocessing, a suitable value according to the calculated offset amountcan be set as the offset correction value of a distortion compensationcoefficient, and also the value of the offset correction unit Ofst_u issuitably adjusted, whereby the offset correction processing can suppressinfluence to be applied to the convergence of a distortion compensationcoefficient in the distortion compensation coefficient updatingprocessing small.

In addition, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 13, the multiple divided addressregions 1201 through 1203 are set within the address region to becorrected, and the distortion compensation coefficient correctionprocesses 1350 through 1370 are individually executed as to the addressregions 1201 through 1203, whereby the offset amounts LUTofst_x1 throughLUTofst_x3 corresponding to the address regions 1201 through 1203 can becalculated.

Accordingly, even in the event that the frequency of occurrence of thetransmission signal Tx(t) has bias regarding the power value p(t), amore accurate offset amount according to the power value (address value)thereof can be calculated as to the distortion compensation coefficientwithin each LUT. Thus, unbalance regarding an offset amount causedwithin the address regions to be corrected of the respective LUT can bereduced, whereby the distortion compensation coefficient offsetcorrection processing within the respective LUT can more accurately becontrolled.

Accordingly, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 13, the precision of thedistortion compensation coefficient offset correction processing withinthe respective LUT can be improved.

Note that, with the flowchart in FIG. 13, though an example employingthe distortion compensation coefficient correction processing accordingto the first embodiment illustrated in FIG. 6 has been illustratedregarding the distortion compensation coefficient correction processes1350 through 1370, the present disclosure is not restricted to this, andfor example, the distortion compensation coefficient correctionprocessing according to the second embodiment illustrated in FIG. 8, ordistortion compensation coefficient correction processing according tothe third embodiment illustrated in FIG. 10 may be employed, forexample.

5. Fifth Embodiment

Hereafter, description will be made regarding a wireless communicationdevice and a distortion compensation apparatus, according to a fifthembodiment.

5-1. Configuration Example of Pre-Distortion Signal Generating Unit 1422

Though the configuration of a wireless communication device 1400according to the fifth embodiment differs from the configuration of thewireless communication device 300 illustrated in FIG. 3 in that adistortion compensation apparatus 1402 and a pre-distortion signalgenerating unit 1422 are provided instead of the distortion compensationapparatus 302 and pre-distortion signal generating unit 322, portionsother than those are the same. Accordingly, with regard to theconfiguration of the wireless communication apparatus 1400, drawingthereof is omitted.

FIG. 14 is a diagram illustrating an example of the internalconfiguration of the pre-distortion signal generating unit 1422. FIG. 15is a diagram for describing the distortion compensation coefficientcorrection processing at the pre-distortion signal generating unit 1422.Hereafter, a configuration example of the pre-distortion signalgenerating unit 1422 will be described with reference to FIGS. 14 and16.

Though the internal configuration of the pre-distortion signalgenerating unit 1422 differs from the internal configuration of thepre-distortion signal generating unit 1122 illustrated in FIG. 11 inthat an offset control unit 1432 and an offset correction processingunit 1470 are provided instead of the offset control unit 1132 andoffset correction processing unit 1170, and further, an address regiondetermining unit 1460 is provided, portions other than those are thesame. In FIG. 14, the same or corresponding portions are denoted withthe same reference numerals as with the pre-distortion signal generatingunit 1122 illustrated in FIG. 11.

As illustrated in FIG. 14, the pre-distortion signal generating unit1422 includes a distortion compensation coefficient supplying unit 450,a distortion compensation processing unit 460, and an offset correctionprocessing unit 1470. The offset correction processing unit 1470includes an offset control unit 1432, compensation value storage units1135 through 1137 and 1139 through 1141, offset compensation units 1138and 1142, and an address region determining unit 1460. The offsetcontrol unit 1432 includes a mean value calculating unit 434 in the sameway as with the offset control unit 1132.

With the offset correction processing unit 1470, the address regiondetermining unit 1460 receives the generated address Adrs(Tx(t)) fromthe address generating unit 402 based on the power value p(t) of thetransmission signal Tx(t). The address Adrs(Tx(t)) is signals having anaddress value corresponding to the power value p(t) of the transmissionsignal Tx(t). The address region determining unit 1460 monitors thereceived address Adrs(Tx(t)) for a certain period of time (or a certaintimes of counts worth) to count the frequency of occurrence for everyaddress value. The address region determining unit 1460 calculates, asillustrated in FIG. 15, an occurrence frequency distribution of theaddress value corresponding to the address Adrs(Tx(t)) based on theresult of the counted occurrence frequency.

The address region determining unit 1460 divides the address region tobe corrected of each LUT into multiple address regions based on thecalculated address value occurrence frequencies. The address regiondetermining unit 1460 performs processing for dividing the addressregion to be corrected into a predetermined number of regions so thatthe totals of address value occurrence frequencies in the multipleaddress regions after division are mutually equal, thereby determiningthe region made up of the individually divided address regions. Theaddress region determining unit 1460 divides the address region to becorrected of each LUT into three address regions 1501 through 1503 asillustrated in FIG. 15.

The address region determining unit 1460 obtains the value of an addressserving as a boundary of the multiple divided address regions, and setsthe obtained address value as a boundary address value adrsTHn (n is aninteger equal to or greater than 1). For example, as illustrated in FIG.15, the address region determining unit 1460 obtains the value A_(th12)of an address serving as a boundary between an address region 1501 andan address region 1502 (the minimum value of addresses within theaddress region 1502), and sets the obtained A_(th12) as a boundaryaddress value adrsTh1. Also, the address region determining unit 1460obtains the value A_(th23) of an address serving as a boundary betweenthe address region 1502 and an address region 1503 (the minimum value ofaddresses within the address region 1503), and sets the obtainedA_(th23) as a boundary address value adrsTh2. The address regiondetermining unit 1460 outputs address region information ADR includingthe set boundary address value adrsThn to the offset control unit 1432.

The offset control unit 1432 receives the address region information ADRfrom the address region determining unit 1460, and sets multiple dividedaddress regions within the address region to be corrected of each LUTbased on the received address region information ADR. The offset controlunit 1432 sets the boundary address value adrsTHn included in theaddress region information ADR as a parameter used for processing suchas the offset correction processing or the like, thereby setting themultiple address regions.

The offset control unit 1432 sets the three address regions 1501 through1503 illustrated in FIG. 15 using the above boundary address valueardsTh1 and boundary address value adrsTh2, for example.

Accordingly, the distortion compensation apparatus 1402 determines therange of each of the address regions within the address region to becorrected based on the address value occurrence frequency distributionobtained by monitoring the address Adrs(Tx(t)) generated based on thepower value p(t) of the transmission signal Tx(t), whereby a divisionmode of address regions of the address region to be corrected can bechanged according to difference in a communication environment where thedistortion compensation 1402, and the wireless communication deviceincluding the distortion compensation apparatus 1402 are disposed, andthe ranges of the address regions can be optimized. Thus, the distortioncompensation coefficient offset correction processing within each LUTcan more accurately be controlled as compared to the distortioncompensation apparatus 1102.

Accordingly, with the distortion compensation apparatus 1402, theprecision of the distortion compensation coefficient offset correctionprocessing within each LUT can further be improved as compared to thedistortion compensation apparatus 1102.

Note that, with the above embodiment, though the address regiondetermining unit 1460 calculates an address value occurrence frequencydistribution based on the address Adrs(Tx(t)) received from the addressgenerating unit 402, the present disclosure is not restricted to this.For example, an arrangement may be made wherein the address regiondetermining unit 1460 receives the address Adrs(T(t−1)) from the delayunit 404, and calculates an address value occurrence frequencydistribution based on the received Adrs(T(t−1)).

Also, with the above embodiment, though an example has been describedwherein the address region to be corrected is divided into three addressregions, the present disclosure is not restricted to this, and thenumber of address regions to be divided can be changed as appropriate.

5-2. Example of Distortion Compensation Coefficient Correction andUpdating Operation at Distortion Compensation Apparatus 1402

FIG. 16 is a diagram illustrating an example of a flowchart ofdistortion compensation coefficient correction and updating processingat the distortion compensation apparatus 1402 according to the fifthembodiment. Hereafter, description will be made regarding the distortioncompensation coefficient correction and updating processing that thedistortion compensation apparatus 1402 executes, with reference to theflowchart in FIG. 16. Note that, with the flowchart in FIG. 16, anumeric expression relating to the processing in the corresponding stepis indicated in a portion surrounded with a dotted line.

First, in step S1602, the distortion compensation apparatus 1402 startsa series of the distortion compensation coefficient correction andupdating processing.

Next, in step S1604, the address region determining unit 1460 setsparameters used for occurrence frequency counting processing as initialsetting. Examples of the parameters to be set include a number of timesN (number of times of frequency counting) of processing for counting thefrequency of occurrence for every address value based on the addressAdrs(Tx(t)) (occurrence frequency counting processing). Now, let us saythat this number of times of frequency counting is N₀ (N₀ is a positiveinteger). Also, the address region determining unit 1460 sets “0” as theinitial value of a number of times i of the occurrence frequencycounting processing.N=N ₀i=0

Next, in step S1606, the address region determining unit 1460 determineswhether or not the number of times i of processing is greater than anumber of times N of frequency counting. In the event of the addressregion determining unit 1460 having determined that the number of timesi of processing is greater than the number of times N of frequencycounting, the processing proceeds to step S1612. In the event of theaddress region determining unit 1460 having determined that the numberof times i of processing is equal to or smaller than the number of timesN of frequency counting (not greater than the number of times N offrequency counting), the processing proceeds to step S1608.

Next, in step S1608, the address region determining unit 1460 receivesthe address Adrs(Tx(t)) from the address generating unit 402. Theaddress Adrs(Tx(t)) has the address value generated based on the powervalue p(t) of the transmission signal Tx(t) at the current referencepoint-in-time t. The address region determining unit 1460 counts forevery address value the frequency of occurrence thereof based on thereceived address Adrs(Tx(t)).

Next, in step S1610, the address region determining unit 1460 incrementsthe value of the number of times i of processing by “1”, therebyupdating the number of times i of processing. After updating of thenumber of times i of processing, the processing returns to step S1606.

Next, in step S1612, the address region determining unit 1460 calculatesan address value occurrence frequency distribution as to the addressAdrs(Tx(t)) based on the occurrence frequency counted in steps S1606through S1610. The address region determining unit 1460 divides theaddress region to be corrected at each LUT into three address regionsbased on the calculated address value occurrence frequency distribution.The address region determining unit 1460 performs processing fordividing the address region to be corrected into three regions so thatthe totals of the occurrence frequencies of address values in thedivided multiple address regions are mutually equal, thereby dividingthe address region to be corrected into three address regions 1501through 1503 as illustrated in FIG. 16.

The address region determining unit 1460 obtains the value of an addressserving as a boundary of the multiple divided address regions, and setsthe obtained address value as a boundary address value adrsTHn (n is aninteger equal to or greater than 1). The address region determining unit1460 obtains an address value A_(th12) serving as a boundary between theaddress region 1501 and the address region 1502 illustrated in FIG. 16,and sets the obtained address value as a boundary address value adrsTh1,and also obtains an address value A_(th23) serving as a boundary betweenthe address region 1502 and the address region 1503, and sets theobtained address value as a boundary address value adrsTh2.adrsTh1=A _(th12)adrsTh2=A _(th23)

According to the above steps S1604 through S1612, address regiondetermination processing 1640 as to the address region to be correctedis performed at the offset correction processing unit 1470.

Next, in step S1614, the offset control unit 1432 sets parameters usedfor offset correction value setting processing, offset compensationvalue updating processing, and offset correction processing inlater-described steps S1618 through S1622. The details of the parametersto be set are as described with the flowchart in FIG. 13. However, theboundary address values set in step S1612 are set as the boundaryaddress values adrsTh1 and adrsTh2, respectively.

Next, in step S1616, the offset control unit 1432 selects one LUT to beprocessed out of the LUTa 406 through LUTd 412. The offset control unit1432 cyclically selects the corresponding LUT in the sequence of LUTa406, LUTb 408, LUTc 410, LUTd 412, LUTa 406, LUTb 408, and so on, forexample.

Next, in step S1618, the offset control unit 1432 executes distortioncompensation coefficient correction processing 1650 as to the addressregion 1501 of the selected LUT_x to be processed (x is any of a throughd). This distortion compensation coefficient correction processing 1650is the same as the distortion compensation coefficient correctionprocessing 1350 described in steps S1308 through S1314 in the flowchartin FIG. 13.

Next, in step S1620, the offset control unit 1432 executes distortioncompensation coefficient correction processing 1660 as to the addressregion 1502 of the selected LUT_x to be processed. This distortioncompensation coefficient correction processing 1660 is the same as thedistortion compensation coefficient correction processing 1360 describedin steps S1316 through S1322 in the flowchart in FIG. 13.

Next, in step S1622, the offset control unit 1432 executes distortioncompensation coefficient correction processing 1670 as to the addressregion 1503 of the selected LUT_x to be processed. This distortioncompensation coefficient correction processing 1670 is the same as thedistortion compensation coefficient correction processing 1370 describedin steps S1324 through S1330 in the flowchart in FIG. 13.

A series of processing performed in the above steps S1604 through S1622is the distortion compensation coefficient correction processing thatthe distortion compensation apparatus 1402 executes.

Next, in step S1632, the compensation coefficient updating unit 324performs distortion compensation coefficient updating processing as tothe respective LUT. The details of this distortion compensationcoefficient updating processing are as described with the flowchart inFIG. 6. After the distortion compensation coefficient updatingprocessing, the processing returns to step S1616.

In step S1616, the offset control unit 1432 selects another LUT out ofthe LUTa 406 through LUTd 412 as the next LUT to be processed. Theoffset control unit 1432 executes the distortion compensationcoefficient correction processes 1650 through 1670 as to the addressregions 1501 through 1503 regarding the selected LUT to be processed.

As described above, with the distortion compensation coefficientcorrection and updating processing illustrated in FIG. 16, in the sameway as with the distortion compensation coefficient correction andupdating processing illustrated in FIGS. 6 and 13, according to theoffset amount calculation processing and offset correction processing, adistortion compensation coefficient is clipped to the upper limit orlower limit of the coefficient setting range, whereby the distortioncompensation performance can be suppressed from deterioration. Further,according to the offset compensation value updating processing, even inthe event that the value of the distortion compensation coefficientstored in each LUT is corrected by the offset correction processing,suitable distortion compensation processing can be performed using adistortion compensation coefficient generated in a pseudo manner.

Further, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 16, in the same way as with thedistortion compensation coefficient correction and updating processingillustrated in FIGS. 6 and 13, according to the offset correction valuesetting processing, a suitable value according to the calculated offsetamount can be set as the offset correction value of a distortioncompensation coefficient, and also the value of the offset correctionunit is suitably adjusted, whereby the influence of the offsetcorrection processing to be applied to the convergence of a distortioncompensation coefficient in the distortion compensation coefficientupdating processing can be suppressed small.

Further, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 16, in the same way as with thedistortion compensation coefficient correction and updating processingillustrated in FIG. 13, the offset amounts LUTofst_x1 through LUTofst_x3corresponding to the address regions 1501 through 1503 of the addressregion to be corrected can individually be calculated, whereby thedistortion compensation coefficient offset correction processing withineach LUT can more accurately be controlled even in the event that thefrequency of occurrence of the transmission signal Tx(t) has biasregarding the power value p(t).

In addition, with the distortion compensation coefficient correction andupdating processing illustrated in FIG. 16, according to the addressregion determination processing 1640, an address value occurrencefrequency distribution is calculated by counting the frequency ofoccurrence for every address value based on the address Adrs(Tx(t)), andthe range of each address region within the address region to becorrected is determined based on the calculated address value occurrencefrequency distribution. Thus, the address region dividing mode of theaddress region to be corrected can be changed according to difference ina communication environment where the distortion compensationcoefficient correction and updating processing is performed, and therange of each address region can be optimized. Thus, the distortioncompensation coefficient offset correction and updating processingwithin each LUT can more accurately be controlled as compared to thecase of the distortion compensation coefficient offset correction andupdating processing illustrated in FIG. 13.

Accordingly, with the distortion compensation coefficient offsetcorrection processing and updating processing illustrated in FIG. 16,the precision of the distortion compensation coefficient offsetcorrection and updating processing within each LUT can be improved ascompared to the distortion compensation coefficient offset correctionand updating processing illustrated in FIG. 13.

Note that, with the above embodiment, though counting of the frequencyof occurrence for every address value has been carried out by a certainnumber of times of counting worth, thereby calculating an address valueoccurrence frequency distribution, the present disclosure is notrestricted to this, and an address value occurrence frequencydistribution may be calculated by carrying out counting of the frequencyof occurrence for every address value for a certain period of time forexample.

Though description has been made so far regarding a wirelesscommunication device, a distortion compensation apparatus, and adistortion compensation method, according to an exemplary embodiment ofthe present disclosure, the present disclosure is not restricted to thespecifically disclose embodiments, and various modifications and changescan be made without departing from the scope of the claims.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A distortion compensation apparatus forperforming distortion compensation processing by applying inverseproperties of distortion properties of a power amplifier to atransmission signal to be input to the power amplifier, comprising: aplurality of distortion compensation coefficient storages configured tostore a plurality of first distortion compensation coefficients used forsaid distortion compensation processing; and circuitry configured tosubject each of said first distortion compensation coefficients storedin each of said plurality of distortion compensation coefficientstorages to offset correction processing that corrects each offset forthe each of the distortion compensation coefficients, generate one ormore second distortion compensation coefficients corresponding to saidoffset correction processing not having been performed from the firstdistortion compensation coefficients that have been subjected to theoffset correction processing based on generated delay at a particularreference time, the first compensation coefficients being stored in thedistortion compensation coefficient storages corresponding to thetransmission signal at different times, and subject said transmissionsignal to said distortion compensation processing based on said one ormore second distortion compensation coefficients.
 2. The distortioncompensation apparatus according to claim 1, wherein said circuitry isfurther configured to: calculate an offset amount of each of said firstdistortion compensation coefficients as to each of said plurality ofdistortion compensation coefficient storages to perform said offsetcorrection processing based on said calculated offset amount, calculatean offset compensation value as to each of the first distortioncompensation coefficients after said offset correction processing basedon said calculated offset amount; and generate said one or more seconddistortion compensation coefficients corresponding to said offsetcorrection processing not having been performed and said offsetcompensation value to supply said one or more second distortioncompensation coefficients for said distortion compensation processing.3. The distortion compensation apparatus according to claim 1, whereinsaid circuitry calculates an offset amount of each of said firstdistortion compensation coefficients as to each of said plurality ofdistortion compensation coefficient storages, and when said calculatedoffset amount is a value out of a predetermined range, subjects thecorresponding first distortion compensation coefficient stored in thecorresponding distortion compensation coefficient storage to said offsetcorrection processing.
 4. The distortion compensation apparatusaccording to claim 1, wherein the circuitry is further configured tosearch a maximum power value of said transmission signal; and whereinsaid circuitry changes an address region to be corrected within thecorresponding distortion compensation coefficient storage where saidoffset correction processing is performed, based on the maximum powervalue of said transmission signal determined by said search.
 5. Thedistortion compensation apparatus according to claim 1, wherein each ofsaid plurality of distortion compensation coefficient storages includesa plurality of address regions to be corrected where said offsetcorrection processing is performed; and wherein said offset correctionprocessing is performed independently for every said plurality ofaddress regions to be corrected.
 6. The distortion compensationapparatus according to claim 5, wherein the circuitry is furtherconfigured to: generate an address of the corresponding distortioncompensation storage based on a power value of said transmission signal;and count a frequency of occurrence for each address value of saidgenerated address to determine said plurality of address regions to becorrected within the corresponding distortion compensation storage basedon said counted frequency of occurrence.
 7. A distortion compensationmethod for performing distortion compensation processing forcompensating distortion of a power amplifier as to a transmissionsignal, comprising: performing offset correction processing as to aplurality of first distortion compensation coefficients stored in eachof a plurality of distortion compensation coefficient storages; readingout said first distortion compensation coefficients according to a powervalue of said transmission signal from said plurality of distortioncompensation coefficient storages; generating one or more seconddistortion compensation coefficients corresponding to said offsetcorrection processing not having been performed from the firstdistortion compensation coefficients that have been subjected to theoffset correction processing based on generated delay at a particularreference time, the first compensation coefficients being stored in thedistortion compensation coefficient storages corresponding to thetransmission signal at different times; and performing said distortioncompensation processing as to said transmission signal based on said oneor more second distortion compensation coefficients.
 8. The distortioncompensation method according to claim 7, further comprising:calculating an offset amount of each of said first distortioncompensation coefficients as to each of said plurality of distortioncompensation coefficient storages; and calculating an offsetcompensation value as to each of the first distortion compensationcoefficients after said offset correction processing based on saidcalculated offset amount; wherein, with the performing of said offsetcorrection processing, said offset correction processing is performedbased on said calculated offset amount; and wherein the generating ofsaid one or more second distortion compensation coefficients is based onsaid offset compensation value.
 9. The distortion compensation methodaccording to claim 7, further comprising: calculating an offset amountof each of said first distortion compensation coefficients as to each ofsaid plurality of distortion compensation coefficient storages; andperforming said offset correction processing as to the correspondingfirst distortion compensation coefficient stored in said correspondingdistortion compensation coefficient storage when said calculated offsetamount is a value out of a predetermined range.
 10. The distortioncompensation method according to claim 7, further comprising: searchinga maximum power value of said transmission signal; and changing anaddress region to be corrected within said corresponding distortioncompensation coefficient storage where said offset correction processingis performed, based on the maximum power value of said transmissionsignal determined by said searching.
 11. The distortion compensationmethod according to claim 7, wherein a plurality of address regions tobe corrected where said offset correction processing is performed areset to each of said plurality of distortion compensation coefficientstorages; and wherein, with the performing of said offset correctionprocessing, said offset correction processing is performed independentlyfor every said plurality of address regions to be corrected.
 12. Thedistortion compensation method according to claim 11, furthercomprising: generating an address of said corresponding distortioncompensation coefficient storage based on a power value of saidtransmission signal; and counting a frequency of occurrence for everyaddress value of said generated address to determine said plurality ofaddress regions to be corrected within said corresponding distortioncompensation storage based on said counted frequency of occurrence. 13.A wireless communication device comprising: a distortion compensationapparatus configured to perform distortion compensation processing byapplying opposite properties of distortion properties of a poweramplifier as to a transmission signal to be input to the power amplifierbeforehand; an up converter configured to perform orthogonal modulationprocessing and also frequency conversion processing to a radio frequencyas to the output signal of said distortion compensation apparatus; andthe power amplifier configured to perform power amplification processingas to the output signal of said up converter; wherein said distortioncompensation apparatus includes a plurality of distortion compensationcoefficient storages configured to store a plurality of first distortioncompensation coefficients used for said distortion compensationprocessing, and circuitry configured to perform offset correctionprocessing as to each of said first distortion compensation coefficientsstored in each of said plurality of distortion compensation coefficientstorages, generate one or more second distortion compensationcoefficients corresponding to said offset correction processing nothaving been performed from the first distortion compensationcoefficients that have been subjected to the offset correctionprocessing based on generated delay at a particular reference time, thefirst compensation coefficients being stored in the distortioncompensation coefficient storages corresponding to the transmissionsignal at different times, and perform said distortion compensationprocessing as to said transmission signal based on said one or moresecond distortion compensation coefficients.